2012: Year of Reliever Whiffs

With due respect to landing a quad, it is believed that one of the hardest things to do in organized professional sports is hit a baseball. Relief pitchers across Major League Baseball are taking that to a new level in 2012.

Since 1961, there have been exactly twelve instances of players registering a strikeout rate above 40%. Five of them are from 2012. While the season is clearly not over yet and we could see declines in strikeout rates, this could be considered the greatest group of relievers, relative to strikeouts, in MLB history.

Looking at the top-ten strikeout rates leaderboard for the last five seasons looks like this:

Season	Name	K%
2012	Aroldis Chapman	47.00%
2012	Craig Kimbrel	45.90%
2011	Kenley Jansen	44.00%
2012	Kenley Jansen	41.70%
2010	Carlos Marmol	41.60%
2011	Craig Kimbrel	41.50%
2012	Ernesto Frieri	40.70%
2012	Jason Grilli	40.30%
2010	Billy Wagner	38.80%
2009	Jonathan Broxton	38.00%

You can see how prominently 2012 is featured here. It’s also interesting that there is but one representative from 2009 and not a single player from 2008. Considering how good Billy Wagner and Jonathan Broxton were in their 2010 and 2009 seasons, it’s also pretty amazing to see how much separation there is between them and Aroldis Chapman, Craig Kimbrel, and Kenley Jansen thus far.

Not that 40% is particularly magical as a strikeout rate, but to accomplish such a level of dominance is pretty rare among pitchers. For relief pitchers, it has been achieved only ten pitchers if we count the first half of 2012. The first time there were two relievers over 40% in a single season was 1999 with Armando Benitez and Billy Wagner. But looking at the top five strikeout rates since 2008 paints an interesting picture:

Season	Name	K%
2008	Grant Balfour	36.60%
2008	Juan Cruz	33.00%
2008	Carlos Marmol	32.80%
2008	Brian Fuentes	32.00%
2008	Octavio Dotel	31.90%

Season	Name	K%
2009	Jonathan Broxton	38.00%
2009	Phil Hughes	33.70%
2009	Michael Wuertz	33.60%
2009	Rafael Soriano	33.20%
2009	Joe Nathan	32.80%

Season	Name	K%
2010	Carlos Marmol	41.60%
2010	Billy Wagner	38.80%
2010	Rafael Betancourt	35.90%
2010	Joaquin Benoit	34.60%
2010	Joel Hanrahan	34.00%

Season	Name	K%
2011	Kenley Jansen	44.00%
2011	Craig Kimbrel	41.50%
2011	David Robertson	36.80%
2011	Sergio Santos	35.40%
2011	Koji Uehara	35.00%

Season	Name	K%
2012	Aroldis Chapman	47.00%
2012	Craig Kimbrel	45.90%
2012	Kenley Jansen	41.70%
2012	Ernesto Frieri	40.70%
2012	Jason Grilli	40.30%

No single season in baseball history has ever featured as many strikeout rates over 40% as 2012. This list could lose two players and still hold true. And if we average out all qualified relievers over the last five seasons, the trend is pretty clear:

Each of the last five seasons has seen about a half percentage point jump in average strikeout rate, with the increase between 2011 and 2012 being the greatest at about 1.5%. But if you look at the top five strikeout rates per year over the last five seasons, the gap widens:

After a fairly steady increase between 2008 and 2011, the jump in 2012 is over 4% among the top strikeout relievers.

We’re just a little over half way to the finish line, so we can’t definitively say 2012 features the most dominant group of relievers ever, but the signs are certainly pointing in that direction. The reasons for such a trend are likely multi-layered, with advances in hitter scouting, better utilization of players suited for short relief appearances, a larger talent pool, luck, among many others. But amidst some of the more obvious (and compelling?) league storylines over the course of the remainder of the season, this is one that will be interesting to see play out.

Note: A special shout-out to Bill McAfee who has the lowest strikeout rate for any reliever on record with a 3.8% rate in 1934.