While updating my numbers on the average run and out values of various batted ball types this past afternoon, I noticed what looked like an anomaly when it came to ground balls in the American League this season. The average run value of a ground ball was roughly half so far in 2010 of what it was in 2007-9. I assumed there had to be something off with my code and my first check was to look at the National League, but that did not turn up any unexpected results.
Curious, I spit out the odds of an out occurring on a groundball in each year as a chart. In years past, right around 66% of all ground balls were turned into a single out. An additional 7% caused a double play. The National League is almost exactly the same though it has had more single outs and slightly fewer double plays on account of there being fewer runners on base on average.
However, so far in 2010, those ratios are up to 68% and 7.5% in the American League while the National League shows no significant deviation. Now, that does not seem like much of a change from average in the AL numbers but consider that a ground ball is the single most likely outcome for any plate appearance. There are lots of them and any movement can reap big changes.
In 2009, hitters batted .239 on ground balls. That’s down to .210 in 2010 and there’s been a rise in double plays turned (and a triple play as well). All that adds up to a lot more outs, about 163 in fact. Over just under 4500 ground balls, you have outs up about 4%, but only in the AL. What’s changed? I have no idea, but right now ground ball hitters are having quite a tough time of it.
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