Concussion Injury Information

With two of the game’s better players, Justin Morneau and Jason Bay, spending considerable time on the DL last year because of concussions, I decided to take a look at how concussions have been reported and the possible effects head injuries might have on player performance. Thanks to the hard work of Matthew Grosdidier, who compiled most of the data, we have some interesting numbers to look at on head-related trauma.

Concussions historically have not been reported as an injury, nor did players go on the DL for them. Recently, though, they’ve been better-diagnosed and players appear to be more cautious about the long-term implications of traumatic brain injuries. From the data I have, the only times players have been put on the DL for concussions are:

1. When they’re hit in the head with a pitch.
2. When they run into an outfield wall.
3. When they collide with other players.

Here are the numbers of players and the days spent on the DL for concussions since 2002:

There have been 50 reported concussions in the majors in the past nine years, with 68% of them being reported in the past four years. There was a jump in reported cases between 2005 and 2007, when players appear to have been more willing to go on the DL for head injuries.

Besides the number of players going on the DL for concussions, I looked at the possible effects that concussions can have on a player’s performance. I wanted to look at players who returned from a traumatic brain injury during the same season in which they went on the disabled list. One huge problem is the lack of data. First, there are only 50 samples. Making matters even more difficult is that some players ended the season on the DL, which doesn’t give congruent time-frames. Additionally, four players’ careers were ended with concussions (Kevin Olsen, Adam Greenberg, Corey Koskie, and Mike Matheny.

The player’s performance before getting a concussion is compared to the 15 and 60 days after the injury. Since the number of games is not uniform, I adjusted the player’s performance to the harmonic mean of the number of plate appearances before and after. Here are the results:

Perhaps not surprisingly, this small sample of players performed worse after their concussion. The drops in SLG and OBP were rather substantial.

There is a not much injury data available on concussions, but the little that is available shows a recent jump in players diagnosed with concussions and those players performed worse after coming back. As more data becomes available, hopefully a better picture concussions can be created.

Injury information is from Josh Hermsmeyer’s injury database (2002 to 2009) and my collection of 2010 DL data.

Jeff, one of the authors of the fantasy baseball guide,The Process, writes for RotoGraphs, The Hardball Times, Rotowire, Baseball America, and BaseballHQ. He has been nominated for two SABR Analytics Research Award for Contemporary Analysis and won it in 2013 in tandem with Bill Petti. He has won four FSWA Awards including on for his Mining the News series. He's won Tout Wars three times, LABR twice, and got his first NFBC Main Event win in 2021. Follow him on Twitter @jeffwzimmerman.

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13 years ago

Yes, Correlation does not imply causation BUT… Koskie, Bay and Morneau are all Canadian and I assume all played hockey (Morneau did for sure). I wonder if there is anything to that.

Of course, the counter point would be that most MLBers were probably pretty good high school football players.

13 years ago
Reply to  Otter

Research in concussions show that once someone suffers a concussion it is more likely for that person to suffer a similar brain injury. However, the brain does often heal if given enough time (up to two years in some cases), the affects have been found to disappear.

The more studies on concussions show that we know very little. Sometimes the worst graded concussions leave little sign of an injury (at least right away, they don’t know if it shows up 20 years from now). And sometimes the lowest grade concussion turns up the worst symptoms.

Also a study in 2007 found that football leads concussions in high school sports, followed in a distance by soccer and cheerleading (don’t drop the girl!), then in a distance, basketball, baseball , hockey. This I’m recalling from memory, but I do remember cheerleading being surprisingly high.

Concussions are scary. They should be taken seriously, and while you can go back out and play, they shouldn’t. This is much easier for Morneau to accept than other players who haven’t earned their money yet.