Groundballs and Slugging Rates by Matthew Carruth February 18, 2010 Beyond noting that ground balls are less damaging on their own than fly balls I also looked into the effects that a pitcher’s ground ball rate has on his home run rates and found no compelling evidence to support the theory that ground ball pitchers suffer higher rates of home runs on the fly balls they do allow. There’s more to damaging run scoring than just home runs though. I went digging further and started looking at slugging percentage allowed on the batted ball types, absent home runs. Looking at line drives that ended up in play, were they more dangerous as a pitcher’s ground ball rate increased? Nope. As it turns out based on the data that I have looked at is that as a pitcher’s ground ball rate goes up, the quality of line drives that he does allow, both the ones that go for home runs and the ones that stay in the park, do not change. Moving on to fly balls however, the first negative trend for ground ball pitchers emerges. Interestingly, though the rate of fly balls that go for home runs appears to fall as a pitcher’s ground ball rate increases, the slugging percentage on the fly balls that stay in the park goes up. Why? I don’t know. Maybe outfielders shade in and more fly balls go over their heads. Maybe there is some systemic shift in the type of fly balls allowed, though it would be weird for them to be hit harder and yet not see an increase in home runs. All told, it does look like ground ball pitchers see a rise in their slugging percentage allowed on non-ground batted balls. The effect is neither large nor overly consistent but it appears to be present. Up next, I look at strikeouts and walks.