He signed with Texas in 2010 and turned in a sub-replacement level performance that included two trips to the DL; his strikeouts plummeted and his walks climbed to a career high in 2010 Clearly, the Athletics will be hoping he can return to his 2008-2009 form, in which averaged 11 strikeouts per 9 innings over the 289 innings he pitched during those two years.
Harden's calling-card has always been his ability to get the strikeout; his control has never been very good (career 4.16 BB/9), and over the course of his career he's been below average at getting ground balls (39.7% overall with no season over 40% since 2006). He's also not very durable, as he hasn't thrown 150 innings or reached 30 starts in any season since 2004. In 2010, his K/9 rate dropped from 11, where it was in 2008 and 2009, to 7.3. The two aspects of his game that were clearly affected the most were his velocity and, maybe not unsurprisingly, his previously superb ability to miss bats.
The charts in this post will only focus on his four-seamer and changeup, which pretty much make up his entire arsenal. I counted 5 two-seamers in 2008, just 2 in 2009, and 24 in 2010 (1025 four-seamers in 2010, which makes for a ratio of about 43:1). I feel pretty good about the fastball classifications, but there may be a few more two-seamers from 2010 that were lumped in with the four-seamers. The charts below shows the velocity distribution by year for Harden's four-seamer and change.
The data in this post are courtesy of Joe Lefkowitz's tool.