Expected innings per year

[Ennder]

Couple people asked for this so I just did some quick searches on baseballreference. Below is a chart showing the number of seasons of data, the number of pitchers who averaged 200+ IP over that stretch and the number that averaged 180+ IP over that stretch (this includes the 200+ guys).

 

1. 34, 69

2. 21, 47

3. 21, 44

4. 21, 36

5. 16, 31

6. 16, 26

7. 13, 27

8. 9, 21

 

So when you sign a pitcher to a 6 year contract the odds aren't that great that he'll stay fully healthy for 6 years. Granted some retire, some haven't been in the league 6 years etc so the number is expected to be somewhat low. You only have to go up to 2 years to find less than 1 pitcher per team who averaged 200+ IP per season. 200+ IP seasons aren't anywhere near a common thing in baseball.

 

Over that 8 season stretch there were a total of 340 seasons of 200+ IP or 42 per year, less than 1.5 pitchers per team and the trend seems to be going down not up. If you look at 180+ IP seasons there have been 562 over the past 8 seasons or 70 per season. Only a little bit over 2 pitchers per team reach 180+ any given year. Go down to 150+ and you find 774 or 97 per season, still just slightly more than 3 per team.

[sbrylski]

To expand on the concept above:

 

I ran a relatively quick study to explore and support how many innings and how much performance can be expected to be lost each year into a multi-year contract.

 

I started by viewing the 2003 pitching leaderboards from six seasons ago, as a five year contract is what C.C. Sabathia was offered by the Brewers, and therefore the timeframe most relevant to this discussion. I selected every player to have thrown over 200 innings that year to be my initial sample. In order to eliminate factors that could have a negative effect on the accuracy of the study, such as player retirement or more extreme talent loss as a player approaches the age of 40, I threw out all pitchers aged 30 years or older. This left 25 pitchers as my final sample, with ages ranging between 22 and 29 and their average age about one year younger than Sabathia's 28.

 

The following is a table of the average number of innings pitched during each season of the 25 pitcher sample.

 

 2003 2004 2005 2006 2007 2008 ----- ----- ----- ----- ----- ----- Innings 216.3 185.5 172.0 142.5 125.1 127.5 % Change -14.3 -7.3 -17.1 -12.2 1.9 Geometric Average % Change per Season = -10.04% 

This result falls in line quite well with other studies I have read on the subject, and the expected loss of 10.04% of innings each season is incredibly close to the generally accepted 10% loss that is often used by baseball statisticians.

 

I also looked at the number of games started each season by my sample of pitchers. Below is the data table.

 

 2003 2004 2005 2006 2007 2008 ---- ---- ---- ---- ---- ---- Starts 33.0 29.2 27.1 23.0 19.8 20.4 Change -3.8 -2.1 -4.1 -3.2 0.6 Average Change per Season = -2.5 

This sample so far has shown that a pitcher's expected number of innings per season should be lowered 9.8% each year and their expected number of starts should be lowered by 2.5. These numbers fit together, as a 9.8% reduction of 200 innings pitched is a reduction of 16 innings, approximately 2.5 starts given an average start is about 6 innings.

 

http://i35.photobucket.com/albums/d175/sbrylski06/pic1-1.png

 

 

While I had the data at hand, I also looked at expected changes in K/9, BB/9, HR/9 and finally ERA. Below are the graphed results.

 

http://i35.photobucket.com/albums/d175/sbrylski06/pic2.png

 

The sample's K/9 rates decreased by 0.127 per season, while their BB/9 rate increased by 0.019 per season. So not only must a club be weary of handing out a lengthy contract to a pitcher in fear of injury and reduced workloads, decreases in performance should be expected as well. Not that its surprising, though.

 

Notice the high level of fluctuation in the HR/9 graph. Partly due to using a modest size sample, but it also is merely an illustration of how much home run rates can vary for pitchers year to year, as home runs are a much less frequent occurrence relative to strikeouts and walks. The HR/9 rates for this sample increased by 0.005 per season.

 

Plug the above three average change in rates into a fielder independent ERA formula, I will use FIP, and we can see the expected change in results from year one to year six.

 

FIP = (13*HR + 3*BB - 2*K) / IP

 

1st Season FIP = 3.99

6th Season FIP = 4.21

 

That's a loss of .22 points of ERA due to diminished skills. If we look at the actual data, the pitchers lost about .1 points of ERA per season, which is even more significant.

 

 2003 2004 2005 2006 2007 2008 ---- ---- ---- ---- ---- ---- ERA 3.82 4.06 4.03 4.67 4.26 4.29 Change -.24 .03 -.64 .41 -.04 

The difference between the FIP estimates and the actual data is likely due in part to the modest size sample, but could also suggest and support that the pitchers are losing other skills each season, such as the capability to suppress their BABIP below league average.

[rluzinski]

Very nice work. For average IP, I'd be a little concerned about including pitchers who simply weren't good enough to get the opportunity to rack up 200 IP a year. I don't think CC will have to worry about that. http://forum.brewerfan.net/images/smilies/smile.gif

 

Did you come across anyone's age curves for pitchers?

[sbrylski]

Very nice work. For average IP, I'd be a little concerned about including pitchers who simply weren't good enough to get the opportunity to rack up 200 IP a year. I don't think CC will have to worry about that. http://forum.brewerfan.net/images/smilies/smile.gif

 

FYI, half my sample had ERA's under 3, and the average ERA was 3.84. No conclusion along with this fact, just saying.

 

Did you come across anyone's age curves for pitchers?

 

I read an interesting tidbit about pitchers aging curves. Basically, any healthy pitcher will, like hitters, get better into their late 20's and then decline. But because there are so many injured pitchers who never recover or return to form, the average age curve for all pitchers is actually positive sloping at every age (ERA on the y-axis). So I just went with a linear trend line.

[rluzinski]

FYI, half my sample had ERA's under 3, and the average ERA was 3.84. No conclusion along with this fact, just saying.

 

Well, that certainly suggests that the effect might by small but I'm sure you could find a could pitchers in your sample that were limited in opportunity by performance. Kind of hard to objectively determine which, after the fact, though.

But because there are so many injured pitchers who never recover or return to form, the average age curve for all pitchers is actually positive sloping at every age (ERA on the y-axis). So I just went with a linear trend line.

 

You mean, the sample keeps getting smaller (starting pitchers fail to qualify by pitching too few innings) but the ERAs go up?

 

Those graphs are great, BTW.

[sbrylski]

You mean, the sample keeps getting smaller (starting pitchers fail to qualify by pitching too few innings) but the ERAs go up?

 

Basically, if I understand you correctly.

 

If all you know is that a player is a pitcher, you can assume that next season his ERA will rise and his IP will decrease, if they pitched a full season the prior year, regardless of age.

 

Here's a study that demonstrates: LINK

 

Those graphs are great, BTW.

 

Thanks. My favorite part is the visual of how BB and HR spike in 2006, as does ERA. And you can see IP sink their furthest below the trend line because of that.