Injury Chances for Strike-Throwers

In the Oct. 15 issue of ESPN the Magazine, Tim Kurkjian wrote this when talking about young pitchers with injury histories:

GM Billy Beane doesn’t require power, he wants outs without walks. Plus strike throwers generally have good mechanics that help prevent injury. Beane also isn’t afraid to go with young pitchers, what at least in theory are less likely than older ones to get injured.

The line that caught my interest is the one that “strike throwers generally have good mechanics that help prevent injury.” I will try to see if any truth exists in that statement.

Immediately, I spotted three chicken-and-egg scenarios that include mechanics, strike throwing and injuries:

Scenario No. 1: Good mechanics equal More strikes and less injuries

Scenario #2: No injuries equal good mechanics and more strikes

Scenario #3: More strikes equal good results, which equal less of a chance of a fake injury.

I think the truth is a combination of all three. I am not going to get into what may be the possibly cause of what. I just want to see if “strike throwers” are less injury prone. It is tough to know if a statement may be true or not until the numbers are run.

I looked for strike throwers using three stats available at FanGraphs, percent of strikes thrown (Strikes/Pitches or Strike%), Zone% (Pitchf/x *) and non-intentional walk rate (NIBB). I had no idea how a pitcher gets labeled a “strike thrower,” but those three stats seemed like a good place to start. To get a base sample of pitchers, I looked at starting pitchers who threw at least 120 innings in one season and then how many of those ended up on the DL the next season. Historically, 41% of these pitchers end up on the disabled list the next season. After rerunning the numbers for this study, the percent chance of a DL trip has gone down to the 37%-to-39% level.

I divided up the three categories into three ranges with a similar number of samples in each grouping to get the percentage of pitchers who ended up on the DL.

% Strikes DL%
>64% 38.3%
62% to 64% 36.5%
<62% 36.3%
Zone% DL%
>51.5% 34.5%
51.5% to 49% 41.2%
<49% 41.4%
<6.5% 36.3%
6.5% to 8% 35.2%
>8% 39.6%

Average values:37% for Strike% and NIBB%, 39% for Zone% (Pitchf/x values)

The only number that sticks out is the >51.5% value for Zone%. I further divided that group of pitchers up and couldn’t find that the DL% decreased any more. I found that the percent of pitchers who went on the DL was 35.3% for a >51% Zone%. I will use the 51% value because it will be an easier number to remember. In 2012, 35 pitchers ** met this criteria of being a possibly healthy pitcher.

While I was only able to find one of the three categories that showed strike-throwers being healthy, I did find that extreme non-strike throwers had a higher likelihood of ending up on the disabled list.

% Strikes DL%
< 60% 45.0%
Zone% DL%
< 47% 49.0%
>10% 49.2%

A Zone % less than 47%, or a NIBB% more than 10%, puts the pitcher in a 50-50 chance of ending up on the DL. While the Strike% value is not near 50%, it still shows a higher injury chance.

For an example, seven pitchers from 2007 to 2011, met all three of the above requirements in a single season.

Name Season IP age Strike% Zone% NIBB% D.L.
Carlos Zambrano 2010 129.2 29 59.1% 46.6% 12.1% Yes
Doug Davis 2007 192.2 32 58.6% 46.5% 10.2% Yes
Daniel Cabrera 2007 204.1 26 58.1% 44.9% 11.1% Yes
Francisco Liriano 2011 134.1 28 57.2% 43.5% 12.5% No
Roberto Hernandez 2009 125.1 29 59.4% 46.4% 11.7% No
Kyle Davies 2009 123.0 26 58.0% 44.2% 12.1% No
Yovani Gallardo 2009 185.2 23 59.2% 45.7% 11.2% Yes

Four of the seven ended up on the DL the next season. Two pitchers in 2012 met all three criteria: Edinson Volquez and Ricky Romero. It seems more than likely one or the other will be sidelined in 2013. Including Volquez and Romero, here is a table of the 25 pitchers who have a high chance of ending up on the DL in 2012 because they couldn’t throw strikes.

Name Season IP age Strike% Zone% NIBB% # of Instances
Edinson Volquez 2012 182.2 29 59.8% 45.7% 12.3% 3
Ricky Romero 2012 181 28 59.0% 46.2% 12.6% 3
Tim Lincecum 2012 186 28 61.2% 45.2% 10.6% 2
Yovani Gallardo 2012 204 26 59.8% 45.2% 9.1% 2
Carlos Zambrano 2012 132.1 31 58.9% 47.4% 12.5% 2
Ubaldo Jimenez 2012 176.2 28 58.8% 48.6% 11.4% 2
Jeremy Hellickson 2012 177 25 62.6% 43.4% 7.6% 1
Luis Mendoza 2012 166 29 60.2% 43.5% 7.9% 1
Josh Johnson 2012 191.1 28 61.6% 44.4% 7.3% 1
Trevor Cahill 2012 200 24 60.8% 44.4% 8.8% 1
Edwin Jackson 2012 189.2 29 62.8% 44.6% 6.7% 1
James Shields 2012 227.2 31 64.3% 44.9% 5.9% 1
Jon Lester 2012 205.1 28 62.2% 45.0% 7.5% 1
Jake Westbrook 2012 174.2 35 63.3% 45.8% 6.9% 1
Shaun Marcum 2012 124 31 63.4% 45.9% 7.4% 1
Stephen Strasburg 2012 159.1 24 63.2% 46.2% 7.2% 1
Jarrod Parker 2012 181.1 24 61.7% 46.3% 8.0% 1
Hiroki Kuroda 2012 219.2 37 62.9% 46.6% 5.5% 1
Jerome Williams 2012 137.2 31 63.5% 46.6% 5.9% 1
Gio Gonzalez 2012 199.1 27 62.0% 46.6% 8.9% 1
Tommy Hanson 2012 174.2 26 62.1% 46.6% 8.7% 1
Yu Darvish 2012 191.1 26 62.3% 47.7% 10.8% 1
Felix Doubront 2012 161 25 62.6% 48.1% 10.0% 1
Matt Moore 2012 177.1 23 63.1% 50.0% 10.0% 1
C.J. Wilson 2012 202.1 32 60.8% 50.7% 10.3% 1

Some big names fill the list, including free agents Edwin Jackson and Hiroki Kuroda.

Gio Gonzalez is an interesting name here, too. In 2011, he had a 59.9% Strike%, 47.3% Zone% and 10.4% BB%. Two of the categories are within the higher injury threshold and one is almost included in it. I am wondering if this was one of the reason Billy Beane traded Gonzalez after the 2011 season to the Washington Nationals.

Some merit does exist from the statement “strike throwers generally have good mechanics that help prevent injury.” Using the a pitcher’s Zone% value (Pitchf/x), some pitchers can be marked for having a less-than-average chance of ending up on the DL. The main fact is that pitchers at the far end of the non-strike-throwing spectrum are more likely to get hurt. These pitchers, who have problems getting the ball over the plate, have a near 50% chance of ending up on the disabled list the next year. Pinpointing exactly who will end up injured is impossible, but some idea of increased chances can be measured. Also Billy Beane is right, again.


* I wanted to use the BIS Zone% values, but the values weren’t consistent enough over the years. Initially, I found 48% of the pitchers with a Zone% less than 45% went on the DL. Then, I looked to see the number of pitchers who would be on the list for 2012. Sixty-three of the 107 possible pitchers made the list. I went back and ran the numbers for each year and got:

2012: 63 of 107
2011: 75 of 124
2010: 54 of 120
2009: 11 of 102
2008: 0 of 111
2007: 10 of 114
2006: 1 of 104
2005: 0 of 122

I found the data were useless.

Using the PITCHf/x zone I ended up with the following values each year:

2012: 18 of 107
2011: 18 of 124
2010: 14 of 120
2009: 14 of 102
2008: 10 of 111
2007: 22 of 114

These values were more consistent and made more sense.

** Kevin Millwood, Erik Bedard, Blake Beavan, Bartolo Colon, A.J. Burnett, Kyle Lohse, Bruce Chen, Bronson Arroyo, Tommy Hunter, R.A. Dickey, Cliff Lee, Chris Capuano, Kevin Correia, Justin Masterson, Ross Detwiler, Zach McAllister, Max Scherzer, David Price, Clayton Richard, Ricky Nolasco, Derek Holland, Jon Niese, Jordan Zimmermann, Madison BumgarnerMatt Harrison, Henderson AlvarezIan Kennedy, Phil Hughes, Justin Verlander, Brandon Morrow, Kris Medlen, Doug Fister, Travis Wood, Chris Sale, Wei-Yin Chen

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Jeff 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 three FSWA Awards including on for his MASH series. In his first two seasons in Tout Wars, he's won the H2H league and mixed auction league. Follow him on Twitter @jeffwzimmerman.

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As you correctly mention, there are all kinds of selective sampling and cause/effect issues that confound an analysis of this data.

To me, the most salient one is this: Certainly some not insignificant percentage of pitchers who threw fewer strikes (had control problems) already had some sort of injury and were just a DL trip waiting to happen.

If that is true then it is sort of in opposition to Kurkjian’s “theory.” I say sort of because it might also be true that when a pitcher is injured but still pitching, his mechanics are altered or are more inconsistent, causing control problems.

The thing I object to, at least without evidence (I’m not saying that it’s not true) is the “common sense” notion that if you have “poor” mechanics, you are more likely to get injured. While “poor” mechanics, by definition, might limit your ability to be a good pitcher (by limiting control, command, and velocity), there is no particular reason that I can think of that it also increases your chances of being injured. In fact, I can come up with a “common sense” argument that poor mechanics can preserve health by not allowing the body to stress itself as much.

I think an interesting thing to look at is pitchers who have a change in their strike throwing ability and see how that relates to their chances of being injured.