Monday, August 17, 2009

Defense Helping Tigers Pitching

In many past posts, I have used the Fielding Independent Pitching statistic (FIP) to estimate what the ERAs of Tigers pitchers should be based on events over which they have the most control: strikeouts, walks, hit batsmen and homers. The idea is to get a predicted ERA independent of a defensive support behind the pitcher. One valuable characteristic of FIP is that it is more predictive of future ERA than ERA itself. Thus, it can be used to identify pitchers which may improve or regress in the future. The FIP statistic is found at FanGraphs.

One criticism of FIP is that it fails to take into account how hard a pitcher was hit. So, Matthew Carruth and Graham MacAree developed another statistic (tRA) which incorporates all the elements of FIP along with batted ball data (ground ball, line drive, infield fly and outfield fly rates). tRA tells us how many runs per game a pitcher should have allowed given all of these rates. The tRA statistic can be found at Stat Corner. Since roughly 92% of runs are earned, we can take the tRA numbers and multiply by .92 to get tERA. tRA and tERA are a bit more predictive of future ERA than FIP but not substantially so. You can learn more about about tRA at the Stat Corner glossary.

The Table below compares the ERA of Tigers starting pitchers to their FIP and tERA. The first thing to notice is that most of the Tigers pitchers have FIPs and tERAs which exceed their ERAs. This is an indication that they may be receiving a good deal of defensive support or some other kind of good fortune. Some of my thoughts on each pitcher are included below:

Justin Verlander is the one Tigers starter whose ERA (3.28) is higher than his FIP (2.81) and tERA (3.10). It would make sense that a high strikeout pitcher would not get as much defensive support as a pitcher who puts the ball in play. Just based on memory, it also appears that he gives up hits in bunches which also would hurt his ERA in comparison to FIP and tERA.

Edwin Jackson has a big discrepancy between his ERA (2.85) and tERA (4.11). Some of that mat be defensive support but it's important to note that his 81% left on base percentage (LOB% at Fan Graphs) is the highest in the league. That is something that help his ERA a lot. Watching games, it seems as if he has the ability to step up his fastball a notch with runners on base so, while it's not likely he can maintain such a high LOB%, I would expect him to remain above average in that respect. He was at 76.1% last year which is also very good. Still, I would expect Jackson's ERA to rise somewhat by the end of the season.

Jarrod Washburn has an ever bigger difference between his ERA (2.95) and tERA (4.62) than Jackson. A big reason for the gap is that he is an extreme fly ball pitcher who pitched most of the season for a Mariners team which had the best defensive outfield in the majors. He doesn't have that benefit with the Tigers and that's likely going to hurt his ERA substantially.

Rick Porcello has a tERA (5.23) which exceeds his ERA (4.34) by almost a run. That is likely partly a result of a ground ball pitcher supported by strong infield defense. The infield defense is still there and he's still developing so I think he can at least maintain his ERA down the stretch.

Armando Galarraga also has a much higher tERA (6.27) than ERA (5.16) so he is likely another hurler benefitting from defense. He also has the worst tERA in the league.

Table: ERA versus FIP and tERA for Tigers Pitchers

























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