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Wandy Rodriguez and the Curve

Wandy Rodriguez is regarded as one of the better starting pitchers in baseball. He was rewarded as such this off-season when the Houston Astros signed him to a three-year, $34 million extension.

However, the left-hander struggled mightily during the first half of the 2010 season. In his first 14 starts, he posted a 6.09 ERA with 52 strikeouts and 34 walks in 75 and one-third innings. In his next 18 starts, he posted a 2.03 ERA with 126 strikeouts and 34 walks in 119 and two-thirds innings. What happened?

At Baseball Prospectus, Christina Kahrl suggested that Rodriguez refined his curve. Using data from Baseball Analytics, we shall find out exactly how Rodriguez changed.

We will start out with some of the results, first looking at the batted ball splits. In the first half, Rodriguez induced 46 ground balls out of 82 total batted balls (56 percent); in the second half, he induced 89 grounders out of 137 total (65 percent). As we can see by the league trends on batted balls (and intuitively), it is significantly harder to hit for power when the ball hits the ground.

Did he change his general location? During the first half, he was hitting the middle of the plate more often overall. His performance against lefties stayed about the same (.276 wOBA to .273) but improved drastically against right-handers (.341 to .290). The heat maps showed that he hit the corners better and even expanded outside of the strike zone.

Wandy Rodriguez, first half vs. RHWandy Rodriguez, second half vs. RH

In both halves, Rodriguez opted not to use the curve in hitters' counts, choosing instead to use them in pitcher-favored and even counts. His performance in pitcher-favored counts did not vary much at all (.257 wOBA to .226) but in even counts, his wOBA allowed dropped from .355 to .283. The heat maps show you the severe change in location as well.

Wandy Rodriguez, first half, even counts vs. RHWandy Rodriguez, second half, even counts vs. RH

Many have tried to explain Rodriguez's second-half transformation, but the answer may simply be that he located his curve better. After a bit of Googling, I could not find out if pitching coach Brad Arnsberg had Rodriguez change his grip -- or arm slot, or anything else for that matter -- but it would not surprise me if that were the case.


Defining the Strike Zone

Can batters define their own strike zones? There is conjecture that umpires will tend to call pitches strikes in locations where batters swing, and balls in locations where batters don't swing.  That may be the case for Jim Thome.  Over the last three season, Jim walked in 16% of his plate appearances, the third highest in the major leagues behind Chipper Jones and Jack Cust (minimum 1300 PA).  So Jim knows when to swing and when to take. The following heat map shows where Jim swings at pitches:

Jim Thome swings, 2008-2010Note that Thome swings less when the pitches are at the top and bottom edge of the strike zone, and more when the pitches are on the insdie and outside corners.  Compare that to where the umpires call balls:

Jim Thome called balls, 2008-2010While not exactly the same, the umpires are giving Jim the benefit of the doubt up and down, where he swings less, but they are penalizing him on the outside corner, where he swings more.  There may be something to batter swings influencing umpires after all.


The Beckett Cutter

Brian MacPherson at the ProJo Sox Blog wonders if Josh Beckett will keep his cutter under new pitching coach Curt Young:

When looking at Beckett's season, the number of cutters he threw stands out right away. The number of changeups stands out, too. The number of fastballs he threw, predictably, dropped from more than 67 percent down to 54 percent. The number of curveballs he threw dropped, too.

"He had time to sit when he was hurt, and he was watching Lester and Buchholz throwing those cutters," Red Sox manager Terry Francona said. "All of a sudden, he started doing that. He'd throw one good one, then he'd throw three bad ones. But that happens. They're human. That's a part of what makes the game interesting."

Beckett's cutter worked well against right-handed batters, as he kept the pitch away:

Josh Beckett, cut fastball versus right-handed batters, 2010That led to a .269/.316/.365 slash line.  Against left-handed batters, however, he left pitches over the plate.

Josh Beckett, cut fastball versus left-handed batters, 2010The lefties ended up slugging .564 against him on his cutters.  Maybe Josh should simply stop throwing them to lefties.