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.

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Jeff writes for FanGraphs, The Hardball Times and Royals Review, as well as his own website, Baseball Heat Maps with his brother Darrell. In tandem with Bill Petti, he won the 2013 SABR Analytics Research Award for Contemporary Analysis. Follow him on Twitter @jeffwzimmerman.

22 Responses to “Concussion Injury Information”

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  1. Otter says:

    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.

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    • JWay says:

      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.

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  2. Resolution says:

    I’d be curious to see how all players fare after returning from the DL. An overall drop in performance as players readjust seems logical (especially if there’s no rehab assignment). It would be easier to parse out how concussions/brain injuries differ from other types of injuries – if they do at all.

    Having said that, I think it is a pretty cool article and the more attention concussions get, the better for everyone.

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    • Matthew G says:

      I wondered about that too and it does seem logical. However, there is some reason to believe that less is known about how to treat concussions and their effect on players than, say, a twisted ankle. The trainers may not keep out a player with a concussion long enough, but they know how to treat the player with an ankle sprain.

      I would be interested to see an overall effect from a trip to DL study.

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  3. Jim Lahey says:

    I’d also figure there would be a lull in stats when you come back from taking a 15+ day vacation.

    I know I can’t remember everything about my job when I’m out of office for a week, I wouldn’t be surprised if they suffered a similiar adjustment period.

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    • Matthew G says:

      That’s a reason why the 60 game sample was taken. You would be surprised though. I think a few players (Morneau if I remember correct) actually did very well the first few games back, then did not do well the rest of the season as a whole.

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  4. Der-K says:

    I’m not sure that you can include Greenberg on this list.

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    • Matthew G says:

      Why not? The only thing he is included for is the list of players whose career was ended by a concussion. I think he fits that profile. He is not affecting any of the other numbers in any way.

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  5. Flharfh says:

    Interesting to see the difference in handling concussions between the NFL and MLB. In the NFL, most players, even quarterbacks, rarely miss more than a week or two after suffering a concussion, while in MLB, 50-100 days missed seems pretty common.

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    • Barkey Walker says:

      MLB contracts pay for years, NFL contracts pay for days on the field. This is why a “top paid” line player might not clear that (even relative to a working stiff who gets 30+ years on the job) in their 3 year career in the NFL.

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  6. Ken says:

    If I am reading that correctly, it seems that players are significantly worse in the 15 days before they have a concussion, as compared to the 60 games before a concussion. Is there something that can explain that – or am I just not reading that table correctly?

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    • Jeff Zimmerman says:

      Some players dropped out of the sample because there was not 60 days afterwards.

      Also, the way harmonic mean works, some layers may be weighted higher in one sample and not in the other.

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  7. astrostl says:

    FWIW, I recall several reports that Jim Edmonds stopped taking his post-concussion meds after he was released by the Padres (39 wRC+ over 100 PAs). He was picked up by the Cubs, and lit it up (platoon-powered 134 wRC+ over 300 PAs).

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  8. Jeff,

    Glad to see you are putting your knowledge to good use! I followed your career closely of course and was sorry to see all the injuries. Your dad would have been very proud of your tenaciousness.

    As for concussions, all i have to say is that baseball is a lot better than hockey. That said, its scary to see what seemed like a little tap from Johnny Mac could put Morneau out for the season.


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  9. zak says:

    Morneau has had multiple other concussions from his hockey days its scary to think he wont come back as strong but even worse to think 1 more and his career is most likely over. Hopefully he is not like Koskie, though it was really nice to hear Koskie was finally over symptoms years after the injury after getting a new kind of treatment. Hopefully he can come back and not be effected but that might be asking to much.

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  10. Tim says:

    Out of curiosity, what about pitchers who were hit by batted balls during this period? Assuming that at least a couple pitchers were concussed during that period, were they overlooked or excluded as poor comps for Bay and Morneau. Could they tell us anything.

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    • Matthew G says:

      This is a few days old now, and I dont know if you will see it, but there was only one pitcher that we found that had a concussion during this time.

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