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Thursday, August 26, 2004

Unearned Runs Again

I was reading an article on Bill Jame's Win Shares system and although I've read the book I noticed that the article mentioned that unearned runs are split 50-50 between the pitchers and fielders. Based on my previous post on unearned runs I would think that the split would be more like 80% fielders and 20% pitchers. There I noted that the difference in URA between good and bad pitchers along three axes (ERA+, WHIP, and K/9) did show a difference indicating that good pitchers suppress unearned runs as well as earned runs, but that the difference was fiarly small when compared with the total number of unearned runs that score.

Thinking that I had missed something I reran some numbers for 2003 to check my thinking. I reasoned that if unearned runs are primarily or even as much as 50% the fault of the pitcher, then pitchers with high URAs (unearned run average) should be worse pitchers than those whose URAs are low. In other words, bad pitchers will allow opponents to cache in mistakes by the fielders that play behind them so there should be a correlation between high URAs and bad pitchers.

To check this out I found the 76 worst pitchers in URA who pitched over 50 innings and the best 77 pitchers in URA for 2003, roughly the bottom and top quartiles. The worst URA pitchers had a cumulative URA of .716 while the best pitchers were at .100 - a difference of over a half run per game. However, when you look at these two groups their rate statistics are not all that different. For example, their strikeouts per 9 innings are close (6.38 to 7.27), their walks per 9 are close (4.96 to 4.34), their homeruns per 9 are close (1.41 to 1.16), their BABIP is close (.333 to .328), their WHIP is close (1.42 to 1.29) , and the team errors per game are close (.69 to .65). Their ERAs were 4.46 and 4.03 respectively.

Certainly, the high URA pitchers trail in all these categories and are therefore worse pitchers. As I said in my previous post I do think that better pitchers give up proportionally fewer unearned runs, but cumulatively I doubt that these differences could add up to over a half an unearned run per nine innings. After all, the high URA group only gives up just a little over one more baserunner per 9 innings.

In fact, if you reduce the group size to the top and bottom 10% (roughly 30 pitchers in each group) the URA difference climbs to almost a run per game (.999 to .046) but the rate stats don't change.

So what accounts for the differences? I think there are three possible answers:

1) Luck. The high URA pitchers were mostly unlucky. Either their teams committed a lot more errors for them than for other pitchers behind them or the errors happen to come at the wrong time. Either way, they were unlucky. Conversely, the low URA pitchers received good defense that didn't make errors with men on base.

2) Choking. The high URA pitchers pitch well when things are going well but implode when a mistake is made behind them.

3) A combination of both.

At some level the third option must be the correct answer but the hard part is figuring out what the mix is. My intuition would say that luck is the far larger factor here. There may be some players (perhaps Brian Anderson whose 1.64 URA in 2003 was second behind Scott Elarton and who is largely repeating that at 1.35 this season) tend to fall apart when errors are made. If luck is the primary factor then we should be able to detect it since lucks tends to even out with the number of trials which in this case are innings. So let's take a look at the innings pitched:

The average IP for the entire group of 295 pitchers was 119.3, the average of the high URA group was 114.8 and for the low URA group 104.5. The middle group of 142 pitchers had an average IP of 129.7. So both ends of the spectrum tend to include pitchers with fewer innings pitched which would be expected if luck played a role.

You could also look at pitchers with high URAs that also threw a lot of innings and see if these are guys tagged with the "choker" label. The top 10 who threw more than 125 innings are:

                      URA    IP

Brian Anderson CLE 1.642 148.0
Jeremy Bonderma DET 1.000 162.0
Shawn Estes CHN .947 152.3
Ramon Ortiz ANA .850 180.0
Jason Davis CLE .818 165.3
Mark Hendrickson TOR .797 158.3
Mark Buehrle CHA .704 230.3
Andy Pettitte NYA .692 208.3
Joe Kennedy TBA .677 133.7
Jae Weong Seo NYN .670 188.3

In perusing this list none of these pitchers jump out at me as being labeled as having a tendency to implode other than Anderson so I doubt that choking is the primary cause.

You'll also notice that the spread of the top 10 pitchers is quite large which would indicate that we're likely dealing with a significant amount of randomness.

In summary I can say:

1. I still support the idea that good pitchers give up fewer unearned runs given the same misplays behind them

2. That the variation between high and low URA is between half a run and a run per 9 innings for pitchers who've pitched a modicum of innings

3. That the difference in URA is mostly accounted for by luck

4. That the luck probably accounts for 70 to 90% of the difference with the rest being related to the skill of the pitcher primarily related to reducing the number of baserunners per inning*

5. Given the above that the Win Shares system should be modified to assign fielders the responsibility for 85% of the unearned runs and pitchers 15%

* In the previous post I found that the difference in URA between good and bad pitchers was between .050 and .100 depending on how you defined the concept of "good pitcher". So for an average pitcher with an URA of .450 luck accounts for 78-89% of the total.

BTW, here is a great link to Win Shares including current calculations. It's sad to note that Carlos Beltran still leads the Royals in Win Shares with 14 and he hasn't played for the Royals since late June.

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