How have Aluminum Bats changed Baseball?
Statistics for NCAA Division 1 College Baseball 1970-2011

In my article "Why Aluminum Bats Perform Better than Wood Bats I discuss experimental data which shows exactly how much faster some aluminum baseball bats can hit balls compared to wood bats. I also discuss several reasons why aluminum bats outperform wood bats. The controversy over whether or not aluminum bats should be banned for all levels of baseball (including high school and college) has been a hotly debated issue ever since aluminum bats were first allowed in college baseball back in 1974. Concerns over the safety of players - especially pitchers and infielders - and a perceived imbalance between offense and defense are the driving issues behind efforts to ban aluminum bats. Others prefer the "crack" of a wood bat to the annoying "ping" of a metal bat. Regardless of the various viewpoints and opinions which abound, I think it is safe to say that aluminum baseball bats are going to be a part of the game of amateur baseball for a long time to come.

I have heard and read a lot of comments about how metal bats have changed the game of baseball, but until recently I had not seen any hard data to back up such claims. In 2004 I came across statistics published by the NCAA for Division I college baseball starting from the year 1970 through this year. The raw data includes yearly results for batting averages, home runs per game, runs scored per game, strikeouts per 9 innings, pitcher earned-run-averages, stolen bases, and fielding percentages.^[1] A recent article about the 2005 College World Series in the sports section of USA Today^[2] tabulated some of the same data along with a discussion of how hitting (home run production is way down) and pitching (pitching quality and strike outs are up) have changed in recent years.

I have plotted some of the data below and will discuss the trends, but there are several important dates I need to mention which will aid in interpreting the data. First, 1974 was the year aluminum bats were introduced to NCAA college baseball, and metal bats have been used almost exclusively since that year. Secondly, in 1986 the NCAA imposed a lower limit on the weight of a bat. Finally in 1999, after the 1998 season - during which a number of scoring records were broken - the NCAA implemented a performance standard to limit the performance of aluminum and composite bats. I discuss the details of the performance standard for baseball bats elsewhere, but it involves an upper limit on a quantity called the Ball-Exit-Speed-Ratio, a reduction of the maximum barrel diameter to 2.5-inches, the "minus-3" rule on weight which means that the difference between the weight of the bat (in ounces) and the length (in inches) can be nor no more than 3 integers ), and a lower limit on the bat's moment-of-inertia.

More recently, in July of 2009 the NCAA imposed an indefinite moratorium banning the use of composite bats after discovering that composite bats which passed the BESR performance standard were found to exceed the performance standard after being broken in through use. Furthermore, after extensive testing wood, metal and composite bats, and upon the advice of scientists such as myself, the NCAA will be changing the bat performance standard to a new BBCOR=0.5 standard effective January 2011. This new BBCOR standard effectively requires non-wood bats (metal and composite) to produce batted ball speeds exactly the same as wood. As I predicted several years ago, the game of college baseball changed significantly after the BBCOR standard was adopted at the beginning of the 2011 season. Batting averages, home runs per game and earned-run averages are the lowest they have been in more than 30 years.

Batting Averages

The plot at right shows the mean batting average for all NCAA Division I college baseball players as a function of year from 1970 through 2006. It is interesting to note that from 1970 through 1981 there appears to be an almost steady increase in batting average. However, it would be incorrect to extrapolate before 1970 to assume that batting averages have always been increasing from .000 at some point in the past. Instead it is more likely that the mean batting averages in the wood era prior to 1970 fluctuated around a value near 0.265 or so, though even this is speculation. The mean batting average spiked to 0.300 in 1981 and spiked even higher to 0.306 in 1985 before dropping and levelling our around 0.290 for most of the early 1990's. An increase from 0.265 to 0.290 (or higher) is quite significant, and suggests that players using aluminum bats make solid contact with the ball more often than former players did with wood bats. However, as we will see below, during the same time period that batting averages were quickly increasing, pitchers had increasing difficulty strikng batters out, with the number of strikeouts per 9-innings reaching an all-time low in 1981. Pitchers were still struggling in the early 1990's. So, it is difficult to conclude whether the higher batting averages are due primarily to aluminum bats, or poor pitching, or a combination of both. Two things are true. Aluminum bats typically have lower moments-of-inertia than metal bat and therefore may be swung more quickly. A batter who can swing the bat faster has a much higher chance of making contact with the ball since he can wait slightly longer to watch the ball before committing to a swing. Also, since metal bats don't break, many pitches that would have resulted in a broken bat dribbler for an out with a wood bat now result in base-hit singles from an aluminum bat. The drop in batting averages after 1985 may be due to the fact that the NCAA introduced the "minus 5" rule after that year. This rule stated that the numerical difference between the bat weight (in ounces) and the weight (in inches) could not be more than 5 units. A 34-inch bat manufactured in 1986 could weigh no less than 29 ounces. This change would have had an effect on bat swing speeds and might partly explain the immediate drop in batting averages starting in 1986.

But, bat performance didn't stay down. Starting in 1996 batting averages began increasing at a dramatic rate, reaching an record high during the 1998 season. Alarmed by this drastic increase in performance, the NCAA implemented a bat performance standard following the 1998 season. In 1999 NCAA introduced the BESR performance standard, the "minus-3" rule for bat length and weight, introduced a lower limit on a bat's moment-of-inertia, and reduced the maximum allowed barrel diameter. Once bat performance was being controlled through laboratory testing and certification processes, batting averages quickly dropped, and from 2003-2007, batting averages remained relatively constant near the values of the late 1970's and early 1990's.

However, during the 2008-2009 seasons batting averages (and home runs per game) once again began increasing, mostly likely due to the increasing popularity of composite bats. During the 2008 season the NCAA became aware of the fact (well known in the slow-pitch softball world) that the performance of composite bats improves as the bats are broken in through use. This would explain the increase in batting averages and home runs, even as the pitching appears to be improving (data below shows strike outs per game increased a the same time). After conducting several tests, the NCAA discovered that the majority of composite bats being used exceeded the BESR performance standard after been sufficiently used (even the same bats had passed the standard when brand new). In July of 2009, the NCAA passed an immediate and indefinite moratorium banning composite bats until further notice.^[3]

In October 2008, the NCAA announced that the bat performance standard used to regulate the performance of baseball bats would be changing from the current BESR standard to a new BBCOR standard.^[4] This change was implemented after extensive testing confirmed the scientific prediction that non-wood bats which pass the BESR + MOI performance standard can indeed hit balls up to 5-6 mph faster than a high performance wood bat. The new BBCOR requires that all bats must produce a bat-ball-cofficient-of-restitution that equals 0.5 or less - which is the maximum value for a wood bat. From the data I have seen, this means that about 70% of the bats currently on the market in 2009-2010 are no longer be legal for play, and batted-ball speeds for metal bats are no longer be any faster than batted-ball speeds for wood bats.

The effects of the BBCOR=0.5 standard are very obvious. Bye the end of the 2011 season, batting averages dropped almost to pre-aluminum values. This is very significant. Using the new BBCOR bats, players are not putting the ball into play nearly as frequently as they did last year.

Before moving on to look at other data I should point out one other statistic I found which demonstrates that regardless of the bat, good hitters will find ways to make contact with the ball. In 1957 during the wood-only era the best college team batting average was 0.473. In 1994, when aluminum bats ruled the game, the best team college batting average was 0.474.^[5] So, while one could well argue that aluminum bats have helped the average player to make solid contact with the ball more often, the best players in the game are able to hit about the same with wood or aluminum, at least when it comes to batting averages.

Home Runs per Game

The second plot at right shows the number of home runs per game for NCAA Division I college baseball from 1970 through 2006. The data pretty much follows the same trends as the batting average data. However, while batting average indicates how often a player made solid contact with the ball resulting in at least a single or more, the home run data indicates that after aluminum bats were introduced more of the hit balls were going over the fence. There is a steady increase after aluminum bats were introduced, and after a brief surge in the mid 1980's the number of home runs per game dropped and settled to a fairly constant number during the early 1990's. I don't know yet what happened in the early 1980's to produce the surge in home runs, but 1985 was the year the very popular Easton Black Magic baseball bat was introduced.^[6] Metal bat technology improved again after 1995 and the frequency of home runs reached an all-time record high during the 1998 season.^* Then, as was the case for batting averages, the frequency of home runs sharply declined after the NCAA imposed performance limits on bats. By 2007, home run numbers appeared to be settling back close to values during the early 1990's or early 1980's, though they were still significantly higher than in the wood-only era prior to 1974. The sharp increase in home runs per game in 2008 and 2009 is most likely to due an increased popularity of composite bats, which can significantly improve with use. As mentioned above, the NCAA banned the further use of composite bats in July of 2009, but it doesn't appear to have made a significant drop in the number of home runs per game in 2010.

As I had expected, the NCAA adoption of the BBCOR=0.5 bat standard in 2011 has caused the number of home runs per game to drop almost to pre-aluminum values (the lowest number of home runs per game since 1974). This is very significant. Using the new BBCOR bats, players are not hitting home runs with anywhere near the frequency that they did in previous years.

* During the 1998 College World Series between the University of Southern California Trojans and Arizona State University Sun Devils (USC won 21-14) at least 35 out of 111 CWS records were broken and 17 more were tied.^[7,8] Both teams used Louisville Slugger aluminum bats. Records broken during the championship game included runs scored (35), home runs (9), RBI's by one player (7). During the championship series USC also set records for team batting average (.378), runs scored (62), hits (88), and total bases (152).

Strike Outs per 9 Innings

An interesting data set is the number of strike outs per 9 innings for NCAA Division 1 college pitchers. During the same years that batting averages, home runs, and runs scored were increasing, pitchers were having a terrible time getting hitters to strike out. This may not be directly related to the introduction of aluminum bats, and bad pitching may also be part of the reason why batting averages and home runs increased in the years after aluminum bats were introduced to college baseball. Notice, for example, that the number of strike-outs per nine innings dropped by a full strike-out in the three years before aluminum bats were introduced. However, it is true that aluminum bats have had an impact not only on hitting, but also on pitching. One of the biggest impacts of aluminum bats on the pitching game is that they took away the effectiveness of inside pitches.^[9] When a players were using wood bats, a pitcher could throw an inside pitch in attempt to jam the hitter. If the batter made contact with the ball it would likely be on the handle or the taper region of the bat. Balls hit in the handle or taper region of a wood bat don't go very far, and often result in a broken bat. As a result, pitchers could get a lot of players out by throwing inside pitches to batters swinging wood bats. However, aluminum bats don't break for hits on the handle. In fact, many hitters can still put the ball in play beyond the infield when the ball is hit from the handle or taper region of a metal bat. Some of the effects of aluminum bats on pitching can even be seen in the majors. Watch older players like Roger Clemens, or retired pitchers like Ryan Nolan, who grew up in the wood only era and learned to effectively use inside pitches to intimidate batters. They like to throw inside and often intentionally brush back (and sometimes hit) batters who crowd the plate. Many younger batters are used to being able to crowd the plate and get upset when a pitcher throws an inside pitch. And many younger pitchers aren't nearly as likely to throw inside pitches because they have learned through years of experience that inside pitches can be hit (by players using metal bats).

An interesting feature of the strike out data is that the number of strike outs began to increase in the late 1990's and reached an all-time peak in 1999, right around the same time that batting averages and home runs reached their peaks. This would suggest that most players were either hitting long balls for extra bases and home runs or striking out. It would be interesting to see the break down for base hits and doubles compared to home runs and strike outs for the same time period. I would expect to see a drop in base hits.

As a final note the data shows that during the last few years that the number of strike outs per 9 innings is right about the same as it was back in the wood-only era prior to 1974. College pitching seems to be catching up to metal bat technology.

Earned-Run Averages

The historical trend of the earned-run averages for college pitchers pretty much follow the same trends as home runs per game and batting averages. However, the earned-run average data is quite informative, because a comparison between ERA data and the number of strike-outs per 9 innings clearly shows the impact of the bat on the game of college baseball. From 1998 through 2010, the trends for ERA and strike-outs follow similar behavior. In 1998 there were lots of earned runs and lots of strike-outs per game. Both numbers decrease the the next several years, and then both numbers increase again in 2008. But, in 2011, after the BBCOR performance standard was introduced, the number of strike-outs per game remained the same as it has been for the last three years. This would mean that the quality of pitching has remained the same for the last several years. However, the earned-run average has dropped significantly (at the midpoint of the 2011 season it is the lowest it has been in more than 30 years) since the new BBCOR standard was adopted in 2011. This would suggest that while the quality of pitching is roughly the same, the ability of a batter to put a ball into play has dropped significantly.

More Statistics that Players Perform Better with Aluminum Bats

One more set of statistics which illustrate the effect of aluminum bats on the level of play in college baseball comes from the Cape Cod Baseball League, the premier amateur summer baseball league for leading pro prospects. Prior to 1984 players in the CCBL were allowed to use aluminum bats. Starting with the 1985 season the league returned to wood bats only. The graph at right shows batting averages and number of home runs per game from the years 1981-1988. As the data shows, both the mean batting averages and the frequency of home runs per game dropped noticeably after the return to wood.^[9] Most baseball players who successfully make the transition from using aluminum bats in college to playing with wood bats in the pros will agree that if you hit the ball just right with a wooden bat it will go about the same distance as a ball hit with aluminum. The trick is learning to hit the ball just right. With an aluminum bat you can hit the ball almost anywhere along the length of hte bat and still get the ball past the infield. With a wood bat the task is much more difficult.

An interesting 1994 study of Japanese High School baseball players^[10] comparing the wood-only and metal bat eras in Japanese baseball found that after the introduction of metal bats, winning teams had a higher percentage of larger, stronger players. In the wood-only era winning teams won games by getting lots of men on base with well placed singles, moving players by stealing bases and sacrifice bunts, and applying squeeze plays. After metal bats were introduced, winning teams won mostly by relying on the long ball with larger players who had built up muscle mass through weight training and who could take advantage of the hotter metal bats to hit more multiple-base hits and home runs. Both the average player physique and the number of home runs per game increased substantially after the introduction of metal bats into Japanese high school baseball.

Bottom Line

The bottom line is that aluminum bats have had an impact on the game of baseball. Depending on your point of view one could argue that the impact has been either positive or negative. The facts show that batting averages and the frequency of homeruns in college baseball are higher now then they were before aluminum bats were introduced. However, pitchers finally appear to be adjusting and are currently striking out batters with the same frequency as they did in the wood only days. And, the recent restrictions on the performance of bats introduced by the NCAA in 1998 have brought the game back to the level of play in the early 1990's or early 1980's. It is not the same as in the wood only era, but batting averages and home runs are significantly lower than they were in 1998 when metal bat technology threatened to blow the game out of proportion.

References
[1] NCAA Division I Baseball Statistics Trends 1970-2011[ http://fs.ncaa.org/Docs/stats/baseball_RB/reports/TrendsYBY.pdf] (accesssed 9/8/11)
[2] Andy Gardiner, "CWS `good baseball' replaces `gorilla ball': Teams give up power for all-around game," USA Today, page 9C, (June 16, 2005). Permission to attach a PDF file of this article was graciously granted by USA Today.
[3] July 17, 2009 memorandum from the chair of the NCAA Baseball Rules Committee to Athletics Directors, Conference Commissioners and Head Baseball Coaches.
[4] NCAA Changes Measure of Bat Performance posted to the The College Baseball Blog on October 8, 2008. (accessed 4/12/10).
[5] Tom Singer, "Batting Around the Aluminum Debate," SPORT, p. 10 (July, 1995).
[6] Stephen R. Hagwell, "Bat issue goes extra innings in Divisions II and III,"The NCAA News, February 1, 1999.
[7] News article "One, er, several for the books: USC, ASU set or tie 52 records in championship game," posted on CNNSI.COM website on September 3, 1998. (accessed 5.26.05)
[8] Advertisement for Louisville Slugger TPX aluminum bats in Yankees Magazine, 20, p.81 (1999).
[9] P. Gammons, "End of an Era", Sports Illustrated, 112(10), 16-23 (July 24, 1989).
[10] Hayato Uchida, Yoshio Mino, Akira Babazono, Takanori Ogawa and Hideyasu Aoyama, "Comparative Analysis on teh Physique and Batting Records of the Players in the National Summer High School Baseball Tournaments Before and After the Adoption of Metal Bats," Acta med. Okayama, 48(4), 217-223 (1994).

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How have Aluminum Bats changed Baseball? Statistics for NCAA Division 1 College Baseball 1970-2011