The Dave Duncan Effect by Steve Sommer April 16, 2010 Last week Dave, in his piece on Real Groundball Rates, and Erik, in a piece on Brad Penny’s first start, referenced Dave Duncan’s ability to get his pitchers to generate a great deal of groundball outs. In fact in Dave’s summary of the Cardinal’s organizational ranking he specifically referenced Duncan’s ability to take pitchers off of the scrap heap and turn them into serviceable MLB starters with his pitch to contact philosophy, and cited it as one of the reasons for the Cardinals recent success. With all of that in mind I thought it would be interesting to investigate how the batted ball data supports these positions, and what is the magnitude of the effect. My methodology was a simplified version of Tom Tango’s WOWY. I found the difference between each pitchers’ ground ball rates for the two years after he joined the Cardinals and the two years before he joined (if available). Then I found the weighted average (weighted by the lesser of the two sets balls in play) of said differences. I limited the sample to just starting pitchers as that is who people reference when discussing Duncan’s “Magic”. With that in mind here’s the sample Pitcher With-Without Brett Tomko 0.8% Mark Mulder 2.8% Jeff Suppan 2.4% Todd Wellemeyer -10.5% Kip Wells 2.2% Jason Marquis 8.7% Chris Carpenter 11.9% Kyle Lohse 6.2% Joel Pineiro 9.1% The weighted average of the difference works out to ~4.5%, so Duncan’s pitch to contact reputation is backed up by the data. All but Wellemeyer showed improvement in GB%, even Mulder who was a GB pitcher before coming to St. Louis. Clearly this analysis doesn’t speak to overall quality of pitching (for that see this piece by Kincaid) as groundballs and improving groundball rates aren’t the be all end all; however it has been a key component to the Cardinals success in the Tony LaRussa / Dave Duncan era.