Everyone loves having relievers that can strike batters out in their bullpen, guys that can record outs all by themselves without the help of their defense. That comes in handy when there are men in base, since it's really hard to score without putting the ball in play. Take David Robertson of the Yankees for example; he faced 19 batters with the bases loaded last season and struck out 14 of them. Great way to prevent runs.
The pool of unsigned free agent relievers is at least 30 pitchers deep, but not all of those relievers are strikeout guys. We're going to take a look at those with an affinity for strike three using two metrics: K/9 and K%. You're probably familiar with K/9, which is strikeouts per nine innings. The league average was 7.13 K/9 in 2011, and Kenley Jansen led all qualified relievers with 16.10 K/9. The second metric, K%, is simply the percentage of batters faced that the pitcher struck out. It's a more accurate measure of strikeout proficiency. The league average was 18.6% in 2011, and Jansen again led all qualified relievers at 44.0%.
As you'll see below, the K/9 and K% leaderboards are similar but not identical. More efficient pitchers will have a higher K%, even though they may have a lower K/9 than their baserunner-prone counterparts. Here are lists of unsigned free agent relievers with above average K/9 and K% rates.
Strikeouts Per Nine Innings (K/9)
- Kerry Wood - 10.06
- Ryan Madson - 9.20
- Mike Gonzalez - 8.61
- Michael Wuertz - 8.55
- Juan Cruz - 8.51
- Chad Durbin - 7.77
- Fernando Rodney - 7.31
Dan Wheeler just missed the cut with a 7.11 K/9. He would have posted an above average 7.30 K/9 with just one more strikeout last year, and I'm sure an umpire robbed him of a strike three call somewhere along the line. Free agent closer Francisco Cordero struck out a well below average 5.43 batters per nine innings last year.
Strikeouts Per Batters Faced (K%)
- Wood - 25.5%
- Madson - 25.2%
- Cruz - 23.0%
- Gonzalez - 22.2%
- Wuertz - 19.8%
- Wheeler - 19.4%
- Durbin - 18.6%
Rodney (17.3%) drops off the list in favor of Wheeler, which essentially means that more of the outs he recorded were strikeouts, but Wheeler was more efficient and struck out a higher percentage of the batters he faced. Make sense? Cordero was again well below average at 15.3%.