ERA Regression In Action

The Mets' bullpen has generally been regarded as a strength in the early going. A low ERA and an impressive showing in the 20-inning affair are responsible for this perception. However, ERA is a poor statistic for pitcher evaluation and is especially poor when assessing reliever performance. More telling numbers are needed to gauge how the bullpen has fared. Here are some statistics and National League ranks for the Mets bullpen, prior to last night's game:

ERA FIP xFIP BABIP LOB%
Number 2.11 4.30 4.66 .241 89.5%
NL Rank 2 7 12 Lowest Highest

 

(Primers on some of these stats: FIP, xFIP, BABIP. Also, LOB% stands for left-on-base %.)

The stellar ERA masks some less attractive peripherals. It's not exactly correct to say that the bullpen has been lucky. It's more appropriate to say that if the bullpen's defense independent pitching performance remains at the same level, it is unlikely that ERA will stay so low. Average BABIP is usually in the .290-.300 range, and average LOB% is somewhere around 72%. As these numbers regress, runs allowed will likely increase. Here are the same stats after last night's game, which saw the bullpen allow six earned runs in four innings of work:

ERA FIP xFIP BABIP LOB%
Number 2.88 4.58 4.82 .256 85.2%
NL Rank 2 10 13 2nd Lowest Highest

ERA shot up, BABIP increased and LOB% decreased. Anything can happen in one game but this is a microcosm of what is expected to occur, should peripheral statistics remain at their current levels. The crazy walk totals (6.07 BB/9) are the biggest problem. It's doubtful that Pedro Feliciano and Francisco Rodriguez will each continue to walk more than seven batters per nine innings -- walk rate should also regress. Regardless, it's a curious early performance for a staff that had such poor control in 2009 and was instructed to renew its emphasis on throwing strikes during spring training.

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