Baseball bats

It’s spring, when a young man’s fancy turns to baseball.

The NCAA (and high schools, I think) changed their standards for baseball bats this year, apparently in response to safety concerns about people (especially pitchers) being hit by fast-moving balls. The change took effect back in January and was decided on long before that, but I just heard about it.

Descriptions of the change are very confusing, at least to a naive physicist. An example:

So they adopted a standard called the Ball-Bat Coefficient of Restitution (BBCOR), which provides a more accurate measure of bats in lab tests than the old standard, the Ball Exit Speed Ratio (BESR). Rather than measure the ball’s speed off the bat, BBCOR testing measures the collision between the bat and the ball to see how lively the bat is.

That distinction is way too subtle for me! What does “how lively the bat is” mean, if it doesn’t mean how fast the ball leaves the bat?

To be more specific, the coefficient of restitution, by definition, is a measure of what fraction of the mechanical energy that was present before a collision remains after the collision. Having a standard that restricts the  speed of the ball (following a collision under controlled circumstances) is precisely the same thing as having a standard that restricts the energy after the collision (i.e., the coefficient of restitution).

Where’s the Physicist to the National League when you need him?

Of course, even if the two standards are essentially equivalent, changing from one to the other might be a way to tighten up the standard, without making it explicitly obvious that that’s what you’re doing. Maybe that’s all that’s going on here.

You can actually read the old and new standards, equations and all, if you feel like it. It turns out, as far as I can tell, the headline change, from “exit speed” to “coefficient of restitution,” really is a bit of a red herring. The COR is a bit of a cleaner thing to measure, because the old standard had to be measured on a sliding scale for different bat sizes, and the new one doesn’t, but fundamentally they’re measuring essentially the same thing.

The more important point is that they’ve also added an accelerated break-in procedure to the protocol. Apparently composite bats get springier over use (I guess as the materials get compressed). The old procedure tested them new; the new procedure breaks them in first, so that you can’t buy a standards-compliant bat and later end up with one that’s too springy for the standard.

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Ted Bunn

I am chair of the physics department at the University of Richmond. In addition to teaching a variety of undergraduate physics courses, I work on a variety of research projects in cosmology, the study of the origin, structure, and evolution of the Universe. University of Richmond undergraduates are involved in all aspects of this research. If you want to know more about my research, ask me!

9 thoughts on “Baseball bats”

  1. I think I figured it out. I linked my name to the article. Money quote: “… for a given bat length, batted-ball speed is a near-perfect correlation with BBCOR.”

    In other words, they agree with you. BBCOR and BESR are the same thing. What they are doing is negating the effect of bat length.

  2. My comment is extremely random, but I HAVE to post that I never knew so much thought went into a baseball bat. Wow…the things you across reading blogs!!! If there is a Physicist to the NBL, I Nominate you, Ted. Wouldn’t that be a dream come true? 😉


  3. Ted, to give you an update, in the 2011 college baseball season, the University of Texas’s baseball team hit a grand total of 17 home runs. In the 2010 season, they hit a total of 81 home runs. In 2009, 53 home runs, 2008, 60 and 2007 69 home runs.
    I believe high schools adopt the rule in 2012.
    I do not know the difference between BBCOR and BESR, but I do know that 81 home runs is a lot more than 17.
    It will be interesting to watch injury rates over the next few years to see if BBCOR is working.

  4. I will say the past college season was interesting…

    As a high school coach I believe the records in the books at the current time will be the same for the next ten years.

    I’ve noticed the BBCOR bats have less of a trampoline effect than in the past years.

    And the BBCOR bat doesn’t allow for rolling the barrel to make the barrel hotter in the sweet spot.

    With this new technology destroying power numbers in college and can just imagine what will happen at the high school level.

    Players at the high school level have not built up their bodies or they have not matured enough to wield BBCOR bats.

    It’s sad to say that high school baseball may turn into a snore fest.

    I can just imagine balls barely leaking into the outfield or pitchers throwing no-hitters on a regular basis.

    The hittting will be dead…but at least pitchers will be able to set and smash records knowing they can throw it out over the middle of the plate anytime they want.

    Thanks for this post, very informative and well researched.

    Coach Bucher owner of Top Level Hitting

  5. The act of hitting a baseball requires more than just luck. A baseball player must combine both hand eye coordination and physics in order to make contact with the ball. In the MLB the average pitcher throws between 90-95 mph fastball, which takes a mere .4 seconds to reach the plate. As a batter, in this split second you must react to the pitch coming at you. First a batter must decide if they are going to swing at the pitch or not, and if they are going to swing, at which angle the bat should contact the ball at. If the bat makes contact with the lower half of the ball a pop up will occur, the top half and a ground ball will occur. The ideal place to hit the ball is in the center, which most likely will cause a line drive. The plane of the bat during the swing is the variable which determines the angle of the projectile of the ball after making contact with the bat.

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