Can Jason Hammel Keep Handling Lefties?

The Yankees’ decision to bench Alex Rodriguez has consequences extending beyond Game 5 of the 2012 ALDS, win or lose. Staying in the here and now, it’s a decision by the Yankees to prioritize the platoon advantage — with Eric Chavez at third base instead of Rodriguez, the Yankees will be throwing seven left-handed (or switch-hitting) batters at Orioles starter Jason Hammel. Only Derek Jeter and Russell Martin will bat from the right side.

Joe Girardi is betting against a trend from this season’s New And Improved Jason Hammel: against 257 lefties, he allowed a .262 wOBA; against 236 righties, he allowed a .306 mark.

Perhaps Girardi is looking at Hammel’s history. Hammel has never had a devastatingly wide platoon split — he’s not Justin Masterson — but left-handed hitters have always been above average against him, recording wOBAs of .333 or better every season prior to 2012.

But Hammel has significantly altered his pitching style in 2012. He spent most of his career as a typical fastball-slider-curve-changeup pitcher, throwing 60 percent fastballs and working off that pitch. This season, he’s halved his fastball usage and thrown in a power sinker to fill the gap. The sinker has added a new wrinkle for Hammel — it has induced grounders on 62 percent of balls in play and created a new dimension to his fastball. Both pitches come in at the same speed, but one dips whereas the other rises, leading to fewer line drives on the four-seamer (14 percent against 21 percent in 2011 per Brooks Baseball).

So this helps explain his success in general, but the addition of a sinker doesn’t explain his success against left-handed hitters. Back in 2010, Max Marchi produced a piece on platoon splits which revealed the sinker has the second-widest normal platoon split of any pitch in the game — over a full run per 100 pitches in favor of the opposite handed hitter. The trend continues this season — lefties have a .360 wOBA against righty sinkers league-wide compared to just a .319 mark from right-handed hitters.

Lefties have actually handled Hammel’s sinker relatively well this season, hitting .264 with a .458 slugging percentage (five doubles, three homers) but have struggled with the more neutral fastball, notching just a .175 average and .290 slugging percentage. They face the pitch just as often and make contact just as often. Although it’s difficult to tell the difference in real-time — both pitches have nearly the exact same velocity and release point, the sinker has more horizontal movement away from lefties and in on righties — it could be worth watching if Hammel shelves the sinker in exchange for the straight fastball against Yankee lefties tonight.

With his lineup tonight, Joe Girardi is betting Jason Hammel’s new pitching style gives us more information than his new platoon statistics. Given Hammel hasn’t even faced 300 batters on either side this season, Girardi is probably making the correct choice in stacking the lineup with lefties. Now it’s up to those lefties to do something with Hammel’s pitches, primarily the sinker that has become the bread to his fastball’s butter.

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That’s very strange, that a pitcher would add a sinker, suddenly do better against lefties by a wide margin, and have the sinker be the least successful pitch. Very counter-intuitive.