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July 12, 2006

Pitcher Run Values (and some other stuff)
by SG

As promised, here are the run values of the Yankee pitchers so far in 2006. This is another math and statistics heavy post, so if you don't care for math, come back another day.

This table is sorted in terms of runs saved above average in descending order. As you can see, Mike Mussina has been the most valuable Yankee pitcher so far this season. His total of 21.9 RAA (runs above average) ranks him as the fifth most valuable pitcher in the American League so far. Mariano Rivera is 13th, and Chien-Ming Wang is 19th.

The process to calculate this is very similar to the process used to calculate a batter's value. I am again using linear weights and assigning values to each event that a pitcher allows, be it a hit, walk, or out. This is then compared to what the league average pitcher would have allowed over the same number of plate appearances (batters faced). I found an error in Jaret Wright's RAA that was posted the other day, he's actually been -1.7 RAA, which is close enough to average anyway. Let's hope he keeps it up. The peripherals are pretty favorable thanks to the 0 BB, 10 K game he just had.

Here's a little more background information on the other numbers that are in here that may not be familiar to all of you.

FIP is fielding independent pitching, which is basically a quick and easy way to regress the impact of a pitcher's performance to remove the impact of balls in play. It is focused on BB, HR, and K and the formula is listed above. FIP says Randy Johnson has pitched better than his ERA this season, which is a good indicator for the second half of the season. Kyle Farnsworth is another player who seems to have been underperfoming his underlying peripherals so far.

xFIP is the same as FIP, except you replace the HR component with 11% of flyballs, which is the standard correlation between HR rate and flyball rate. All flyballs are not created equal, and this stat is fairly new, so the jury is still out on how predictive or useful it really is.

ERA+ is a stat used to compare a pitcher's ERA to the league average ERA in that pitcher's home ballpark. To calculate it, you divide the pitcher's ERA by the league average ERA and then multiply it by 100. For example, Mike Mussina has an ERA of 3.24. The AL average ERA is 4.55. We adjust that to reflect the fact that Yankee Stadium has played as a slight pitchers' park, which lowers it to 4.50. Then we divide 4.50 by Mussina's 3.24 and multiply it by 100, and get Mussina's ERA+ of 139.

BABIP is an acronym that stands for batting average on balls in play. The league average BABIP is .295. It is believed that the ability of most major league pitchers to control this number is limited although some people like Mariano Rivera consistently demonstrate control over it. You can look at this number to see if a pitcher may have been lucky or unlucky so far. Farnsworth's BABIP is pretty high, so we may be able to expect better performance going forward.

HR+, BB+, and K+ are similar to ERA+, in that they are a comparison of a pitcher's HR allowed, walks allowed, and strikeouts per batters faced compared to the league average. Greater than 100 is good, less than 100 is bad.

For example, Chien-Ming Wang has faced 517 batters and allowed 7 HR. I park-adjust the HRs based on the Yankee Stadium HR factor which is 1.03 (Yankee Stadium boosts HRs slightly). This just means that I divide HR by 1.015 (half the games are on the road). I then divide the adjusted HR total 517 to get his HR/BF, in this case it's .013. I divide the league average HR/BF by this number, to get the value 2.18, which is then multiplied by 100. This means Wang is 2.18 times better at preventing HRs than the average pitcher. BB+ is calculated the same way, and K+ is calculated by dividing the pitcher's K rate by league average instead (this is to keep everything on the same scale). So Mike Mussina's BB+ of 175 means he is 1.75 times better than average in terms of walk rate, and his K+ of 135 is 1.35 times better than average in terms of striking out hitters, all in terms of rates per batters faced. The higher these three columns are, the better I think a pitcher can project going forward, as they are all indicators of his ability in the aspects of the batter/pitcher confrontation that he has direct control over.

AVG, OBP, and SLG are the performance of opposing hitters against said pitcher. If you want to see how bad Aaron Small was this year, check out the .333/.401/.650 line against him. Basically, opposing hitters were Albert Pujols against him. If you want to see how sweet Mariano Rivera is, check the Womacking .200/.250/.238 line against him.

That's it in a nutshell. If you have any questions, ask away.