Over the winter, I wrote a lot about measurement of run prevention. In short, run prevention is measured by runs allowed per game and can be divided into two parts: pitching (FIP) and fielding (DER).
Fielding Independent Pitching (FIP) measures pitcher performance essentially independent from fielding. The formula is HR*13+(BB+HBP)*3-K*2)/IP plus a league specific factor to make it equivalent to ERA. The idea is that the contribution of pitching to overall team defense can be derived, for the most part, from walks allowed, strikeouts, homeruns allowed and hits batsmen issued. Note that HR=home runs allowed, BB=walks allowed, HBP=hits batsmen, K=strikeouts and IP=innings pitched.
Defensive Efficiency Ratio (DER) is the percentage of times batted balls are turned into outs by the team's fielders, not including homeruns. There are different versions of the formula but the one now most commonly used is DER=(BFP-H-K-BB-HBP-0.6*E)/(BFP-HR-K-BB-HBP) where BFP = batters faced pitcher, H=hits allowed, K=strikeouts, BB=walks allowed, HBP=hits batsmen and E=errors.
The table below compares the ERAs and FIPs of Tiger starting pitchers in 2006 so far. The DER column is the DER of the team when that pitcher is pitching. FIP-ERA is the difference between the FIP and ERA. A positive number for FIP-ERA indicates that a pitcher may be pitching better than his ERA and might not be getting a lot of defensive support. A negative number indicates that a pitcher may be pitching worse than his ERA and might be benefiting from a lot of defensive support. LOB% is the percentage of base runners allowed that are left stranded. LOB% does not really explain anything about defensive support. I added it to the table because I found it to be interesting and it helped to fill a gap in the analysis.
Table: FIP Analysis for Tiger Starters
As most people know by now, the Tigers have been better at preventing runs than any team in the league so far. They have allowed 3.51 runs per game compared to a league average of 5.03 and they are nearly a run per game better than any other team. The Chicago White Sox are second at 4.33. Their dominance also shows up in ERA where they are 3.22 compared to the league average of 4.77. They also have the best DER in the league (.728 compared to a league average of .694).
Their pitching, as measured by FIP, is also strong but less dominant than the ERA would indicate. Their 4.35 FIP is less than half a run better than the league average (4.77) and second to the Indians (4.31). It’s surprising that the Indians would be number one in FIP given that they are 9th in fewest runs allowed but they are suffering from poor defense (11th in league) and perhaps some bad luck.
But let’s get back to the Tigers. Their FIP is 1.13 higher than their ERA which tells me that their low ERA is somewhat deceptive. It says that their pitching seems to be benefiting substantially from the fielding behind them. Looking at the individual pitchers, Jeremy Bonderman, who has the highest ERA(4.57) among the 5 starters, has the lowest FIP (3.37). All of the other starters have a FIP more than a run higher than their ERA so it seems that most of the staff is getting very strong support from their fielders.
Why is Bonderman different from the rest of them? He is not getting nearly as much fielding support (.704 DER) as Justin Verlander (.753), Kenny Rogers (.739) or Nate Robertson (.735). However, he is getting similar support to Mike Maroth (.706) and he is getting better support than league average (.694). So, it must be more than lack of fielding support in his case. I’m not sure it’s just bad luck either since his ERA has significantly exceeded his FIP every year of his career so far.
Part of the difference between Bonderman and Maroth this year is their LOB% ( 64.3 and 85.5 respectively). Bonderman is allowing more of his base runners to score which could mean that he is allowing bunches of base runners and runs in single innings. The big inning idea is just a theory though and not something which I have researched carefully. I’ll also note that an 85.5 LOB% is an aberration for Maroth as he has not been nearly so high in past years. The other starters also have excellent LOB%s which could be partly a function of a strong bullpen coming in to strand runners in late innings.