Relief Pitcher Disabled List Chances

A few years ago I broke down the disabled list (DL) chances for starting pitchers (39%). I have finally gotten around to making an initial stab at relief pitcher DL values.

The initial problem I have with relief pitchers is defining them. I didn’t want to be looking at pitchers who split their time between a relief and starting role. I decided the pitchers needed to have at least 95% of their appearances as a reliever. Also, I didn’t know what to set the minimum innings limit to. Here is a chart of the DL% depending on the number of innings pitched the previous season. Matched season data from 2002-2003 to 2012-2013 was used.

IP Pitchers Pitchers Who Went on DL DL% Total DL Trips AVG Days per DL Trip AVG Days lost per pitcher
20 2275 741 33% 876 58 22
30 2015 670 33% 798 56 22
40 1744 588 34% 708 55 22
50 1422 487 34% 592 53 22
60 996 337 34% 411 53 22
70 510 157 31% 188 52 19
80 164 43 26% 53 48 16

Not a huge difference in values until a pitcher reaches the 70 and 80 IP level. For all the rest of the analysis, I will use a 20 IP limit (33%) as a baseline. Basically one out of every three relief pitchers should expect to go on the DL for around 55 days. With the average bullpen being seven pitchers deep, the team will need to have two more pitchers who can fill in as the others get hurt (7 * 33% = 2.3 pitchers)

Additionally, it may be counter intuitive that the more innings a pitchers throws their DL chance drops. As I found with starters, if a pitcher has proven they can throw a bunch of innings once, they can probably do it again.

Now on to see about the age component. I looked at the DL chances and days lost with two year time intervals.

Age Pitchers Pitchers Who Went on DL DL% AVG Days per DL Trip
22-23 52 16 31% 65
24-25 214 61 29% 76
26-27 432 121 28% 66
28-29 454 133 29% 54
30-31 348 124 36% 53
32-33 278 104 37% 55
34-35 212 71 33% 64
36-37 147 53 36% 48
38-39 89 37 42% 42
40-41 35 14 40% 48

Some trends can kind of be seen. I went a little further and grouped the data into 5 year grouping where some dividing lines can be seen clearer.

Age Pitchers Pitchers Who Went on DL DL% Total DL Trips AVG Days per DL Trip AVG Days lost per pitcher
20-24 137 40 29% 46 70 24
25-29 1017 291 29% 338 62 21
30-34 741 269 36% 312 56 24
35-39 333 120 36% 151 49 22
> 39 47 21 45% 29 49 30

Two trends stick out now. Younger pitchers are less likely to go on the DL, but when they do, they are more likely to stay longer. The average number of days lost per pitcher (not DL trip) is relatively constant until a pitcher reach the big 40.

So age and previous innings pitched don’t really change a pitcher’s DL chances. Now on to an item which does, previous DL stints.

DL Status Pitchers Pitchers Who Went on DL DL% year2 Total DL Trips AVG Days per DL Trip AVG Days lost per pitcher
DL year1 529 224 42% 308 64 37
No DL year1 1746 517 30% 568 55 18

So relief pitchers who went on the DL in previous season see a 43% increase in their DL chances and when they go on the DL it will be 16% longer compared to the baseline 20 IP values. This increase is important for a bullpen full of injured relievers (see the Rangers). If  a team has all seven of its relief pitchers on the DL in the previous year, it will need three pitchers lined up to fill in (42% * 7 = 2.9).

Well that is it for now. Next up, I will run a logistic regression against the pitcher data to come up with a formula to give each pitcher a DL. Until that date, at least a person now should have a basic understanding of a relief pitcher’s DL chance and the main factor which can increase it, previous injuries.




Print This Post

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.


2 Responses to “Relief Pitcher Disabled List Chances”

You can follow any responses to this entry through the RSS 2.0 feed.
  1. NatsFan73 says:

    Aroldis Chapman: 100% :-(

    Vote -1 Vote +1

  2. eph_unit says:

    cool, cant wait to see the DL% results.

    Vote -1 Vote +1