Dempster Diving

A lot has gone right so far this year for the Chicago Cubs – they have the best record in baseball led by an offense that scores runs in a hurry. It takes more than one breakthrough performance to create this kind of improvement in one winter, and so while the credit has to be passed around, no player’s surge has been more unexpected or helpful than that of Ryan Dempster.

Dempster was a rather pedestrian reliever the last few years with Chicago, missing bats but also having problems finding the strike zone on a consistent basis. Like a lot of right-handed pitchers who use a fastball/slider combination as their two main pitches, he also struggled significantly against left-handers. His career splits vs batter handedness are below:

Vs RHB: .246/.324/.379, 2.09 K/BB, 1 HR per 40 AB
Vs LHB: .280/.386/.456, 1.23 K/BB, 1 HR per 28 AB

With significant platoon splits, relief work seemed the best fit for Dempster, so he could be used primarily against same handed hitters. As a starter, the opposing manager would have the ability to load up the line-up with lefties and let the offense go nuts. There wasn’t much there to suggest that Dempster was going to be a quality starting pitcher.

However, Dempster has taken the challenge of facing more left-handed bats and answered it with gusto. His 2008 splits:

Vs RHB: .193/.295/.289, 1.54 K/BB, 1 HR per 55 AB
Vs LHB: .177/.247/.304, 3.15 K/BB, 1 HR per 32 AB

He has more strikeouts against lefties than he does against righties, and he’s putting them on with the free pass far less often than in years past. His pitch selection doesn’t appear to have changed much, mixing in a change-up (that Lou Piniella calls a splitter and has similar downward movement) about 1/3 of the time against lefties and keeping the slider as a weapon against right-handed hitters.

Whether his change/split has really improved or, more likely, this is just an unsustainable excellent performance, the Cubs have to be thrilled with how the Dempster-to-the-rotation move has worked. He’s not going to post a 2.81 ERA this year, but even a regression to his 3.78 FIP would make him a quality starting pitcher. If he can continue to keep left-handed hitters in check, the Cubs will have found themselves another strong arm to slot in behind Carlos Zambrano in their chase to end the curse of the billy goat.