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David Aardsma, Two Years Later

It was a little over two years ago that Jack Zduriencik traded for David Aardsma, acquiring him away from the Red Sox. Writing up the move at the time, I did not react with much fanfare. In the midst of a winter spent acquiring many such pitchers, a now established pattern, David Aardsma did little to make the care-o-meter dance.

Looking back on the two seasons since however, Aardsma has certainly exceeded all reasonable hopes with Seattle. While many of us may call for him to be traded, that is based on the notion that the 2011 Mariners do not justify investing so much payroll into a closer and that he is only going to get more expensive with each new arbitration hearing. It has less to do with Aardsma's performances, where he has made himself into a bona fide bullpen asset.

How did Aardsma change after the trade to Seattle? Here's David Aardsma pre-2009:

21% K, 14% BB, 3% HR, 38% GB, 4.85 FIP, 5.54 RA

And David Aardsma from 2009-present:

26% K, 11% BB, 2% HR, 28% GB, 3.35 FIP, 3.12 RA

The changes are easy to spot, Aardsma went from a mediocre profile to one of a solid strikeout/walk pitcher albeit with an extreme flyball fetish. The motivator for the change in numbers is likely his shift toward an almost exclusive use of his fastball after coming to Seattle. Before 2009, Aardsma threw his four-seem fastball roughly 74% of the time. That jumped to 83% so far with the Mariners.

We can back that up further with numbers on his location. Aardsma is also throwing higher in the zone. We don't have pitch f/x data for his entire career but comparing 2007-8 and 2009-10, the average pitch thrown by the DA is 1.4 inches higher with Seattle.

Whether that continues into 2011 will be an interesting thing to keep track of and the subject of another post in a few days. As I mentioned in his 2010 retrospective, Aardsma threw his four-seamer much less frequently in the second half of this season and was subject to rumors about a coaching mandate to work his offspeed pitches in more.

The fly ball rate makes Aardsma a little scary to watch at times. Taking his K/BB/GB rates and assigning him a league average home run rate (i.e. look at his xFIP), Aardsma comes out about average for a relief pitcher. However, the strikeout and walk numbers are huge leaps forward and Aardsma is luckily in one of the best parks to keep that rate suppressed and glossy up his perceived value. MLB average is a lot better than what he was and so far a lot better than Fabian Williamson.

All signs point to this being Aardsma's last stint with Seattle. The team is unlikely to be in a pennant chase come the trading deadline and should he return from surgery back to closing, he'll be an obvious trade candidate in July with several other bullpen options available for the Mariners and a desire to re-appropriate that salary elsewhere. If so, here's a preemptive well done to you, David. You serve as an example why gathering all these talented cast-offs can sometimes pay off.