We’ve noted many times over the years that relief pitchers are a fickle bunch. We only get 60 or 70 innings to evaluate each season, making the effort of predicting their future performance an at times futile one. Luke Gregerson was dominant in his first two seasons in San Diego, but despite a drop in ERA, he struggled in 2011. The numbers:

Year Inn. ERA K/9 BB/9 HR/9 FIP
2009 75 3.24 11.2 3.7 .4 2.50
2010 78.3 3.22 10.2 2.1 .9 2.86
2011 55.7 2.75 5.5 3.1 .3 3.40


Gregerson struck out nearly 30 percent of batters in his first two seasons. Last year, his strikeout percentage fell to 14.1. That’s an alarming drop.

Using the new PITCHf/x tool created by Brooks Baseball and The Hardball Times, we can take a quick look inside the numbers. Gregerson relies heavily on the slider and below are some of his numbers for that pitch:

Year SL% MPH Call Str. Swings Whiffs/Swings
2009 51 84.1 15.8 55.3 46.7
2010 59 84.7 17.4 53.3 40.1
2011 54 85.5 13.6 52.3 33.5


Gregerson is still getting batters to swing at his slider, however, when they do swing they are much less likely to miss, as evidenced by the decline in Whiffs/Swings from 46.7 percent in 2009 to just 33.5 percent last season.

It’s also important to note that while Gregerson’s slider velocity has actually increased, his fastball and sinker velocity have decreased over the past three seasons, perhaps making his slider less deceptive and/or allowing batters to wait that much longer to recognize the slider.

Can Gregerson remain successful striking out only 14 percent of batters? It’s unlikely. While his home run rate was excellent in 2011, as he allowed just two home runs all year, that’s almost certainly going to increase in 2012. Only 3.8 percent of his fly balls traveled over the fence last year and that number tends to regress heavily toward the league average (~11 percent).

A sub-two strikeout-walk-ratio and a more normal HR/FB rate will likely lead to an ERA well into the threes. Out of the bullpen and in Petco Park, there just isn’t a lot of value there.

It’s impossible to tell if Gregerson will regain his swing-and-miss ways, but the over-reliance on the slider is worrisome. He missed a month in 2011 with a strained left oblique, and you have to be concerned that further injuries and/or decline in velocity could continue due to the high slider percentage.

Gregerson is a personal favorite and I’m certainly hoping he can regain his 2009-2010 form. Keep a close eye on his early season strikeout percentage and whiff rates for an indicator as to how his 2012 campaign might unfold.