Mariano Rivera’s Curious Rates

With the activation today of Brian Bruney from the disabled list and the designation of Jose Veras, I thought it a particularly good time to check in the end of the line of the Yankee’s bullpen, Mariano Rivera.

The first year into his three-year, $45-million contract, signed about two weeks after he turned 38, Mariano Rivera posted his best strikeout rate since his first full season in the bigs in 1996. And his 12.83 strikeouts to each walk absolutely shattered his previous career best of 6.92. On top of all that personally controlled awesomeness, Rivera also benefited from a .232 BABIP and the lowest hits per batter faced of his career. Add it all up and it is no wonder he posted a 1.40 ERA. His 2.03 FIP showed it was no fluke though.

Move forward to 2009 and how has Rivera done? Well, noticeably worse is easy to see, but there are some frightening numbers beneath the surface. Rivera’s 7.5% swinging strike rate is the lowest on record for him. There has been a sizable dip in the number of pitches thrown within the strike zone and hitters are not chasing these extra balls out of the zone.

Rivera’s ground ball rate is also at its lowest point on record, though that is over a smaller sample than his individual pitch results. It is no surprise then that the home run rate has increased, though the rate by which is has increased is surprising and not likely to continue. Rivera has allowed five home runs already this season through 26.2 innings. The last time he allowed more than five home runs was 1995 when he was a starter.

Interestingly, Rivera’s strikeout and walk rates have not moved much despite the drastic change in his individual pitch outcomes. 32 strikeouts to just two unintentional walks, and no hit batters, gives Rivera an even better ratio than last year. Given his extreme drop in missed bats and overall strikes thrown however, I would not expect that to continue. It will be interesting to see which regression, the strikeout and walk rates or the home run rate, influences Rivera’s final line the most.