Know Your North Side Pitchers - Ryan Dempster

I won't bore you all with the starter -> Tommy John Surgery -> lousy starter -> scary closer -> good starter -> big contract story, you've heard it. The contract Ryan Dempster signed after his return to the rotation seemed about right at the time, as it seemed to reflect an expected decline/regression in performance. No complaints from me, and the guy sure is entertaining.

Sadly, Dempster's new born daughter was born pre-maturely and has had some serious health issues. I'm more than willing to excuse this season's uneven performance, as I'm impressed that he was able to work at all during such hardship.

What Dempster Throws

Dempster used to throw 95, before he blew-up his elbow. These days, he's more like low 90's, but I think he's lost a notch in the early going of 2009. We'll see if he picks up some speed in the warmer summer months, though.

Yet another pitcher who likes the sinking two-seam fastball, Dempster also throws your typical four-seam heater, a slider (which he loves) and a split-fingered fastball. The splitter isn't his only off-speed pitch, as there's a circle-change in the bag that moves a little differently (less) than the trap-door splitter. Demp may have added a cutter this year, too. I've found a dozen and a half of them, but I second pass at his data would be in order to validate it. And maybe some video viewing.

Sidebar: Checking video helps with PITCHf/x classifications. Not sure what a pitch is? Think the system may be producing errors? MLBTV is a handy tool, if you happen to be a subscriber.

Results

Dempster's low 90s heat is off-set very nicely by the low 80s change-up, splitter and slider (which runs closer to 85/86 actually). With a full set of tools, Dempster misses a lot of bats. Based on my latest check of the leaderboard, only Javier Vazquez has posted a higher whiff rate (1000+ pitches in 2009). 29% of the swings taken against Vazquez have found air, followed by Dempster (26.8) and John Danks (26.6).

One of the keys for Dempster appears to be a stat I call "Chase" - it's just swing rate on pitches out of the zone (zone=two foot wide plate, btw). He's 10th in the majors, with 30% of his pitches out of the zone yielding swings.  As you'd expect, that rate is driven by the splitter and the slider, which both check in with Chase rates around 37%, and, combined, they account for 2 out of 5 pitches thrown by Dempster since 2007.

Not only to the splitter and slider get chased 37%, they get whiffed (in or out of the zone) on 36% of swings. Dempster's sinker doesn't move as much as what you saw from Randy Wells, but he throws it harder, and gets about the same overall results (in terms of run value) but with fewer ground balls. In general, though, Dempster doesn't give up too many hard hit balls (check that link out, you'll see the same charts for the Sox in the series wrap-up), he does miss a lot of bats, but he can get wild. Very wild.

Where's the Zone?

Time for a graph. The strike zone I use is a wide zone, two feet. But that's how the hitters see it, and how the umpires call it. The umps are rated on a 21 inch zone, so the notion of a 17 inch plate is rather quaint, given how the game is actually played. To define a "wide zone" I use each batter's top and bottom, as entered by the PITCHf/x operator. They use a tool to line-up the markers for each hitter, but I aggregate all of a player's at bats to arrive at average top/bottom value.

Blah blah blah, here's a timeline of Dempster's In Wide Zone rate (IWZ) since he went back to starting games at the onset of 2008. I'm including a his post-season start, but not his All Star Game appearance (too ugly). Three lines - league average (solid gray), Dempster average (dashed black) and Dempster by game (dark blue, broken between seasons). 

So, he's below average to begin with, and coming off his worst start, command-wise, since 2008. But, just as often as he goes wild, or more often, he pounds the strike zone. You simply don't know which version you'll get, but, clearly, this year it's more likely to be a below-average version of Dempster.

You can read more about Wells and the Cubs at Cubs f/x. I also write at Beyond the Boxscore, The Hardball Times and Out of the Ivy. And just about any place desperate enough for content to invite me over.