How MLB's Understanding of Line Drive Data Fails to Protect Pitchers

Minitab Blog Editor 29 June, 2015

Last month the ESPN series Outside the Lines reported on major league pitchers suffering serious injuries from being struck in the head by line drives, and efforts MLB is making towards having protective gear developed for pitchers. You can view the report here if you'd like:

A couple of things jump out at me from the clip:

  1. The overwhelming majority of pitchers are not interested in wearing protective gear if it is either visually obvious or noticeable to the pitcher himself, who fears it will affect his ability to pitch well.
  2. The standard set by Major League baseball is that approved headgear must be able to protect against a ball travelling at 83 mph, the average speed in which line drives are travelling when they reach the pitcher's mound.

Torres in protective headgearUpon watching the report, I knew immediately it would have little if any impact on pitcher safety and that pitchers will continue suffering severe injuries or even death from line drives until a stronger standard is set and pitchers are forced to wear approved devises. The faulty understanding of statistics has led to the current standard, and I will outline three reasons why.

  1. The standard was set as the average.  First, I would like to say it is commendable that MLB collected data on the ball speeds in order to set the standard rather than just making some intuitive guess. However, that data was then turned into a single value, as is unfortunately so common in the world: the average. I think the problem is that what statisticians call the mean, most people refer to as the "average." When most people hear the term "average" they associate it with a meaning somewhat like "common" or "typical," but to know what is common or typical we must also know about the variation in the data. Assuming line drive speeds are symmetrically distributed, half of them will exceed 83 mph and half will not. Very few will actually be 83 mph, so that value is really not common or typical at all. In selecting this value as a standard, baseball's governing body has determined that head gear does not need to protect against half of line drives.
  2. The standard ignores the relationship between speed and likelihood of striking the pitcher. The standard begins by ignoring half of all line drives. But it's actually worse than that. From #1 you might assume that while the average was not the best choice, cutting the rate of line drives hitting pitchers in the head and injuring them in half is a pretty good first step. But that would assume all line drive speeds are equally likely to hit the pitcher in the head, and that is certainly not the case. A pitcher has twice as long to react to a 60 mph drive as he does a 120 mph drive, which, of course, is more likely to actually hit him. Their analysis assumes the distribution of line drive speeds hitting pitchers in the head would match the distribution of all line drive speeds, whereas almost every instance of a head strike involves the ball travelling faster than the average speed. So the rule protects against line drives that are, for the most part, not actually hitting the pitcher in the head.
  3. The standard ignores the relationship between speed and severity of injury. Aside from a pitcher being much more likely to react to a slower ball and avoid the hit in the first place, that slower ball was likely to be much less damaging if contact was made. The balls travelling very fast—which we've just stated were more likely to hit the pitcher—are also considerably more damaging and most needing of protection.

​So to summarize, setting the standard at the average speed has the effect of protecting pitchers against line drives that are unlikely to hit them and will cause much less damage if they do so. Given that pitchers already don't want to wear protection and will quickly catch on to these facts intuitively (even if they don't think in statistical terms), it's hard to imagine many pitchers adopting the gear if not required, or truly being more protected in any meaningful way if they do.

As Minitab trainer Paul Sheehy was telling me recently, giving someone powerful tools like statistics and not properly training them in how to use them is letting them "run with scissors."  Unfortunately in this case it is major league pitchers who stand to get hurt, and not the people carrying the scissors... 

Photograph of Alex Torres by UCinternational, used under Creative Commons 2.0.