2010 was widely known as the “year of the pitcher”, and for good reason.  There were five no-hitters or perfect games, six if you count the game in which Armando Gallaraga’s perfect game was denied by a missed call by the first base umpire.  No-hitters and perfect games are an odd and rare occurrence, so merely having an unusually high number of them in a single season doesn’t necessarily mean that the pitchers dominated that year.  It could be a statistical anomaly or a year where a few individual pitchers had outstanding seasons.  There are other statistics which point towards dominance of pitchers in 2010 beyond the mere no-hitter count.  The Major League earned run average (ERA) was 4.08, which is the lowest it has been since 1992.  There were an average of 7.1 strikeouts every nine innings, the highest that number has ever been, although it’s just a tick higher than the 7.0 number posted in 2009.

Lots of theories have been thrown around to try and explain the dominance of pitching in 2010. Some say it’s an anomaly. Some say it’s just a continuing trend. Some blame the umpires, and many point to performance enhancing drug testing. All of those are plausible and in combination could be the cause. One thing I haven’t seen put forward as an explanation is the fact that in 2010, there was a change in one of the three most important pieces of equipment used in baseball: the bat.

I was recently looking at the Official Rules of Major League Baseball and on page number four they have a section titled “Changes for the 2010 Major League Season”.  I hadn’t recalled reading anywhere about notable changes to the rule book in 2010, so I reviewed the items to see if any major changes had been made.  The first few changes were about how to draw the lines of the field and the coach’s box, again nothing of real importance.  However, the fourth bullet point read:

“Reduced maximum bat diameter to 2.61 inches.  (Rule 1.10(a))”

So I then went to rule 1.10(a) and read the following:

“The bat shall be a smooth, round stick not more than 2.61 inches in diameter at the thickest part and not more than 42 inches in length.  The bat shall be one piece of solid wood.  Note: No laminated or experimental bats shall be used in a professional game (either championship season or exhibition games) until the manufacturer has secured approval from the Rules Committee of his design and methods of manufacture.”

In the 2009 rules, the bat was allowed to be a maximum of 2.75” in diameter.  The last time the maximum diameter of the bat had changed was 1895 when the size changed from 2.5” to 2.75”. Therefore, the allowable bat diameter shrunk by 5.1% in the off-season immediately prior to the “year of the pitcher” and it was the first time such a change had been made in 114 years.

Click to enlarge to actual size

It would seem pretty likely that such a change would negatively impact hitting, so I reached out to Dr. Rod Cross, a physics professor at the University of Sydney and author of papers titled Performance vs moment of inertia of sporting implements, and scatterings of a baseball by a bat. I asked him what impact the decrease in bat diameter would have on the game.  He responded:

“It should not make any difference to home runs or any other batted balls if the bat strikes the ball near the middle of the bat. The only difference would be in those cases where only the edge of the bat strikes the ball. So, there would be an increase in the number of complete misses or strikes, possibly by the same fraction as the change in bat diameter.”

So he suggests that swinging strikes would increase by about 5%.  I found conflicting numbers in regards to swing and miss strikes on various websites, however theoretically, if there were an increase in swinging strikes, that should increase the number of strikeouts overall.  Strikeouts per nine innings in 2010 were 7.1, which was 1.4% higher than 2009 and 4.4% higher than 2008.  Homeruns per nine innings were a steady 1.0 in 2010, 2009 and 2008.  So on a very surface level, the numbers have shades of what Dr. Cross suggested to me.

Taking the numbers of one season and extrapolating any information based on a rule change, even one seemingly as major as the one described here, is difficult. It will be quite interesting to continue to try and determine if this rule change will have an effect on the game of baseball.  We may never know the cause, if one exists, for the 2010 “year of the pitcher”, however it seems that a once in a 100+ change in the bat certainly is part of the equation.



Some really great questions have been posed by commentariat regarding the reduction in maximum bat size. I wish I had thought of these questions prior to writing the article. They actually never occurred to me. I am still trying to get some follow up questions answered and then I’ll put up some quotes from the people I spoke with. Here’s what I’ve learned so far:

Approximately 35% of Major League players use the maximum diameter bat. I’m still not certain whether that means 35% used something greater than 2.61″ or whether 35% used 2.75″ bats. I’m waiting to clear that one up.

If a player had Major League playing time in 2009, they can use bats they have left over from 2009 which don’t conform to the 2.61″ rule. However they cannot order any new bats that don’t conform.

MLB has people go into clubhouses regularly to test bats for legal diameter and proper wood grain.

Update (2/4 – 9:55):

I got a follow up which informed me that yes, players were grandfathered in if they played in 2009, but not for bats exceeding 2.61″. That grandfather clause was more for the density change in bats, not the size.

Update (2/8 – 11:07):

Rob Neyer has a great piece up regarding my article. He spoke with someone who said there were zero bats in 2009 with a smaller diameter than 2.75″. I was told 35% of players use max diameter bats but still can’t confirm whether it was 2.61″ or 2.75″ diameter they were referring to.

You can follow Nick Scott on Twitter @brokenbatsingle, on Facebook or reach him via email brokenbatsingle at gmail dot com.