Change in pitch selection helped C.J. Wilson’s transition to starter

By Dave Cameron

Editor’s note: Dave Cameron of USS Mariner writes a weekly column for the Brock and Salk blog focusing on baseball from a statistical perspective. Mike Salk writes occasionally for USS Mariner as well.

When the Rangers take the field Friday night for Game 1 of the ALCS, they will hand the ball to C.J. Wilson. A year ago, Wilson was a relief pitcher who hadn’t started a game in the big leagues since 2005. Two years ago, he was a guy who had allowed 35 runs in 46 innings, and there is no way anyone could have convinced you that Wilson would eventually be the guy taking the hill against the Yankees to try to win the pennant.

However, Wilson showed up at spring training, asked to be given a shot in the Rangers’ rotation, and things have worked out for both sides. How did Wilson make the leap from the bullpen to the rotation, and what does his success mean for other relievers who might want to follow in his footsteps? Let’s tackle the first issue, and then we’ll get to the second one next week.

The most obvious change that helped Wilson succeed as a starter was changing his pitch selection. If you scroll down his FanGraphs page you’ll see that he threw more than 70 percent fastballs in each of his first five seasons in the big leagues. His primary second offering was a slider, which he used another 10 to 20 percent of the time. He had a curve and a change-up, but they were used infrequently. He was mostly a fastball/slider guy, and it generally worked pretty well for him.

As a starter, though, he knew that wouldn’t work. In moving to the rotation, his fastball fell to just 49 percent of his total pitches, and in the place of those fastballs, he substituted in a cutter and those sparsely used off-speed pitches. His change-up reached 11.7 percent of his total pitches, double what it was last year, and his curveball usage jumped from 0.6 percent to 8.5 percent. Why did Wilson make these changes? Because the curveball and change-up are both pitches that do well against opposite handed hitters and Wilson now faces a lot of them.

Last year, just 64 percent of the batters Wilson faced were righties, as Ron Washington was able to selectively use him against lefties when necessary. As a starter, though, he has to face whatever line-up the opponents put out, and it’s almost always stacked with right-handers. This year, 80 percent of the batters he faced were right-handed. He couldn’t continue to pitch as a fastball/slider guy and still succeed while facing that many guys who hit from the opposite side.

The types of pitches that a relief pitcher has in his arsenal are a key to understanding whether or not he could make the transition to the rotation. Next week, we’ll take a look at some of the arms in the Mariners bullpen, whether their stuff would allow them to move to the rotation and why some of them are better off staying right where they are.