With yet another brilliant performance Wednesday night against the slugging Blue Jays, Clay Buchholz continues to solidify his breakout 2010 season.
Buchholz is now 13 and 5 with a 2.49 ERA and a ground ball rate over 50 percent. His K/BB rate, however, has been very similar to his 2009 numbers. The biggest difference, and it is a huge difference, is his reduction in home runs allowed.
During his time with the Red Sox in 2008 and 2009, Buchholz allowed 24 home runs in 168 innings pitched. That translates to 1.28 home runs per nine innings. This season, Buchholz has only allowed seven home runs in 118.1 innings or right around half a home run per nine innings.
What has made such a big difference? There are a few factors, but the one that sticks out in my mind is the improvement and increased use of his slider.
Last season, Buchholz used his slider about 10.3 percent of the time. That usage has increased to 19.6 percent currently. Why is he using it more? Because it’s a better pitch.
Using pitch f/x data from TexasLeaguers.com, we can see the increase in vertical movement with Buchholz’s slider.
| Season | Type | Use | mph | V-mov (in) | H-mov (in) | Strike | Swing |
| 2009 | SL | 10.3% | 85.6 | 1.41 | 2.25 | 59.2% | 38.8% |
| 2010 | SL | 19.6% | 89.5 | 5.28 | 1.39 | 63.6% | 52.7% |
The jump in downward movement and increased strike percentage do a couple things. One, the downward movement makes it harder for opposing hitters to elevate the ball (as long as the pitch is located below the belt). Two, both factors have caused hitters to increase their their swing rate on that pitch from 38.8 percent last season to 52.7 percent this season.
Overall, Buchholz has caused hitters to swing at pitches outside the strike-zone over 30 percent of the time this season, which, if it holds up over the final two months, would be his career best in that category (not counting the small 22.2 innings sample size in 2007). The further the pitch gets from the strike-zone the lower the chance for an opposing hitter to make solid contact or contact at all.
The increase in use of both his slider and changeup has in tern made his fastball more effective. According to advanced statistics from FanGraphs.com, all three pitches have held positive values this season.
Those three pitches have accounted for over 90 percent of Buchholz’s offerings this season.
Whether or not Buchholz can maintain his performance next season — due to an xFIP over 4.00 and K/BB rate that is below league average — is not the issue. The improvement we’ve seen from his prior major league experience to this season is what is important. Important for this season’s pennant run and important to know that he should be a reliable part of the Sox rotation for at least the four more seasons that he is under team control.