Pitch f/x: Dan Haren

Dan Haren was traded by Oakland to Arizona this past offseason as part of the rebuilding effort of Oakland and the push by Arizona to solidify their chances in the National League West. His addition gave them a strong 1-2 punch at the front of their rotation with Brandon Webb, allowing Randy Johnson to slot as their #3 starter.

The conventional thinking was that Haren would thrive in the National League, which is traditionally more of a small ball league. However, there were some in the media that looked at the pitching-friendly environment in Oakland and the hitter-friendly environment of Arizona and believed that the difference in leagues would be evened out, or even overcome, by the ballpark differences and that Haren would pitch worse in the NL than he did in the AL.

Well, Haren has, in fact, been signficantly better for Arizona than he was with Oakland last year. His ERA so far is 2.56 compared to 3.07 last year for Oakland. That difference grows to more than a run when you compare his FIP (Fielding Independent Pitching, defined here): this year he's at 2.75, while last year he was at 3.70. He has improved his strikeout rate, his walk rate, his homerun rate and his WHIP this season.

The interesting thing is that the difference does not seem to be due to haren changing leagues. Baseball Reference has a great tool that neutralizes statistics to allow them to be compared across leagues and seasons (their explanation of how it works is here). According to Haren's neutralized statistics, his ERA is still more than half a run better this season.

So why is Haren better? Haren turns 28 years old this September, so the improvement could just be the natural progression of his talent; he is just entering his prime and he is learning how to pitch to major league hitters and how best to utilize his talents. By looking at his Pitch f/x stats we can see exactly what he is doing differently that may account for his improvement.

The first thing to note is that the changes in Haren's pitch selection have been gradual over the last few years. His first year as a starter with Oakland (and coincidentally, the first year that Pitch f/x data was available) was 2005 and he threw 59.2% fastballs. That number has gone down every year since then, to the point where this year he is throwing 50.3% fastballs.

Also, in 2005 Haren was throwing a small percentage of curveballs and changeups. He has gradually worked those out of his repertoire. In 2007 he increased the number of splitters that he threw from 19.5% in 2006 to 22.9%, but those have also decreased this year, down to 20%. So with the decrease in fastballs and splitters and the elimination of curves and changeups, what is he throwing more of?

Well, there aren't too many pitch types left. The answer is sliders and cutters. He has always relied on his slider, throwing it as often as his splitter in 2006 and 2007, but so far this year it has gone up to 23.9%. His cutter was a rare pitch in previous seasons, never even reaching 2%, but this year he has thrown it almost 6%.

I would suggest that this change indicates that Haren is figuring out what works best for him and is paring away all of the other unnecessary pitches. By removing curves and changeups from his arsenal, he can focus on the pitches that work well for him. I also wonder if being around two other dominant pitchers with limited arsenals has worn off on him. Brandon Webb throws about 75% fastballs and Randy Johnson is primarily a fastball/slider guy (with a few splitters mixed in). Regardless of the reasons, Haren continues to improve as a pitcher and is certainly everything the Diamondbacks hoped for when they traded for him this past offseason.