Oswalt’s Mysterious Weapon

Roy Oswalt wasn’t supposed to be this good at age 33. Listed at 6-feet and 192 pounds, Oswalt seemed like a guy who might break down from the rigors of starting every five days — a guy who wouldn’t have a long career.

And, at the start of this season, it certainly looked like he was declining. From 2005 to 2009, his ERA rose from 2.94 to 4.12; last year, he had a career-low in innings (181.1) and strikeouts (138). So it was forgivable to expect a mediocre year.

But the advanced statistics tell a different story: While Oswalt’s overall strikeout was down last year, his whiff rate was higher than it was in 2007. His walk rates have remained strong. FIP, a statistic that strips out batted-ball luck and produces a defense-independent number on the ERA scale, shows a tale of sustained above-averageness. Going into this year, Oswalt wasn’t quite the pitcher he used to be, with FIPs in the low 3s, but he was still a solid pitcher without any obviously declining peripheral statistics.

Now, coming off last night’s complete-game, one-hitter against the Pittsburgh Pirates, it looks like Oswalt has been reborn. His 8.43 K/9 this year is the second-best of his career and 1.5 strikeouts per nine more than last year. His current FIP is the best he’s put up since 2006. He’s talking less about retiring as he did with Buster Olney in 2006, and more about where his team will trade him so that he can compete for a ring.

But figuring out how he’s doing this isn’t easy. Looking at his pitching mix, you can see that he’s used his changeup more this year (12.0 percent), which is twice as much as he has over his career (5.9 percent). It’s strange that using the changeup more would be a good thing, because by linear weights — the FanGraphs’ statistics that evaluate single types of pitches by outcomes — his change-up is not a great pitch. It’s been worth 18.9 runs below average over his career (compared to his fastball at 122.2 runs above average). But is using the changeup now suddenly leading to more strikeouts?

We can tell by linear weights that, even though the changeup is again eliciting below-average results this year (-2.2), the rest of his pitches have put up stronger results with its increased usage. This is where our toolbox comes to an end of sorts. So we have to speculate: Is it because the changeup, though below-average, is setting up the rest of his pitches better? Is it something in the movement of the pitch, or the speed?

It’s not yet in our power to know why Oswalt is striking out more batters, especially since his swinging strike percentage (9.3 percent) has been no different from his career number (9.5 percent). But it does look like the slight change to his mix could be a big factor.