During a discussion on fifth starters, I ended up doing some research on ground balls and their relative worth as compared to non-ground ball batted ball types. What began as a throwaway point has since captured my attention and so I bring some results to you.
First, I looked at batted ball types in complete isolation. I believe it is widely accepted that a ground ball is better than a fly ball from a pitcher’s point of view on average. Arguing whether it is better to be a ground-ball pitcher or a fly-ball pitcher is not the scope in question here. A huge amount of complexity resides in studying such a question, some of which I explore below, but for this first initial look, I just wanted to know nothing more than the relative weight of a ground ball versus a ball in the air on average run scoring.
I need to make a quick note on the terminology here. A ground ball is any batted ball classified as a ground ball or a bunt. A ball in the air is any batted ball classified as a fly ball, a line drive or a pop up. These are my own distinctions. I used the batted ball classifications provided by MLBAM since that is what I had available to me in easy to use database form. I do not expect that the results would be vastly different using other sources since large samples are in play.
I have two sets of information that helped me determine this figure. The first is the average number of outs recorded on each batted ball type. The second is the average run value, derived from changes in score and the run expectancy matrix after each play per batted ball type. For this first isolated comparison I used totals from the American League in 2009. I looked at a couple other years and the National League as well and the numbers change only slightly.
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 additional risk of yielding a home run matters, a lot.
Tomorrow, I am going to look at home run rates in closer detail.