When I posted about the Mariners' 5th starter candidates, a discussion about ground balls broke out and I added a follow-up post based on a quick comparison look between ground balls and fly balls. That post busted a levee of ideas and I ended up delving into tons of data from 2007-9 to look at how different variables interacted with a pitcher's ground ball rate.
I ended up posting a series of articles on the information gleaned on FanGraphs and the thought occurred to me that some of you may not have seen it. I don't like to cross-post material, but since it's been a week and I started it here originally I figured it was worth opening up for discussion.
Ground balls vs. fly balls
Ground balls and home runs
Ground balls and slugging rates
Ground balls and walks and strikeouts
Ground balls and runs scored
I encourage you to go read through them for the graphs at least, but here are some key excerpts:
The results were that the average ground ball generated 0.04 runs and caused 0.80 outs while the average ball in air generated 0.23 runs and caused just 0.62 outs. On a runs-per-out basis, balls hit into the air created almost 7.5 times as much offense as balls kept on the ground did.
What constitutes a line drive is somewhat fuzzy and open to subjective bias. However, even with ignoring line drives, fly balls and pop outs by themselves generate an average of about 0.1 runs and cause 0.79 outs. That rate is still about three times more offensive than the average ball hit on the ground.
The best rule of thumb I can state from this look is that a pitcher’s ground ball rate has no impact on his various rates of yielding home runs and what impact there is might actually be negative.
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.
The expected difference between the two biggest reasonable extremes in ground ball rate (30% to 60%) amounts to fewer than five strikeouts or walks over 200 innings pitched.
To re-state, all data came from MLB 2007-9 seasons and pitchers were restricted to those with at least 250 total balls in play over that entire span.