In theory, line drive rate is a great statistic. Line drives result in hits far more frequently than any other type of batted ball, and thus measuring the frequency at which a hitter sprays a line drive seems worthwhile. Put another way, a line drive produces 1.26 runs per out while a fly ball produces 0.13 runs per out and a ground ball produces just 0.05 runs per out. However, a deeper look reveals some flaws in this line of thinking.
Steve Staude created a neat little tool that correlates almost every hitting stat imaginable. Thanks to Steve, we can see how line drive rate correlates with important hitting stats. Line drive rate has a year-to-year correlation of .36. Right off the bat (pun very much intended) it's evident that this might not be the most reliable statistic. The correlation with wRC+ is even weaker at just .19. Furthermore, the correlations with AVG and BABIP don't even reach .50, and there is a negative correlation between line drive rate and HR/FB.
Looking at the line drive rate leaderboard for the last six seasons reveals that three of the top ten line drive hitters are average or worse. The second highest line drive rate since 2008 belongs to Ruben Tejada, who owns a .259/.323/.319 line for an 81 wRC+.
Given this information, it would appear that line drive rate, at least in its publicly available form, isn't all that useful. Here are three reasons why.
1. Three batted ball categories just isn't accurate enough.
For example, this laser is categorized as a ground ball (H/T to Jeff Sullivan). I'd be willing to bet this ball left the bat at a higher speed than the vast majority of line drives. Within the three batted ball categories, there doesn't tend to be a whole lot of differentiation between individual players. Over the last six years, the spread between the lowest line drive rate and the highest line drive rate is 14.1-25.8 percent. Meanwhile, the spread on HR/FB ratios ranges from 0 (thanks Ben Revere) to 26.1 percent. Peter Bourjos, who has the second lowest line drive rate, has been roughly a league average hitter. There are plenty of in-between hit types, and smashing all batted balls into one of three categories inevitably loses something in translation.
2. Not all line drives are created equal.
As former BtBS writer Max Weinstein so aptly noted, an Omar Vizquel line drive isn't worth as much as a Yasiel Puig line drive. This is pretty intuitive, a Puig line drive is far more fearsome than a Vizquel line drive, or almost any other hitter's line drives for that matter. Furthermore, a Puig line drive is more likely to result in extra bases. Without data such as batted ball velocity, Puig's line drives get lumped together with Vizquel's.
3. Home runs are usually not line drives.
There have been a total of 28,680 home runs over the last six years. Just 4,057 of them, or 15.2 percent, have been classified as line drives. Home runs might have gotten a bit of a bad rap in the sabermetric community in recent years, as one dimensional players such as Mark Trumbo and Nelson Cruz hit plenty of dingers while being otherwise mediocre. Still, good hitters tend to hit them more frequently than other hitters. The correlation between Home runs and wRC+ is .68, and the correlation between HR/FB and wRC+ is essentially the same. In general, good hitters leave the yard pretty often, and they usually hit plenty of fly balls in doing so.
Maybe someday Hit f/x info will enlighten the masses, but until then it's safer to just leave line drive rate by the wayside.
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Chris Moran is a former college baseball player and current law student at Washington University in St. Louis. He's also an assistant baseball coach at Wash U. In addition to Beyond The Box Score, he contributes at Prospect Insider and Gammons Daily. He went to his first baseball game at age two. Follow him on Twitter @hangingslurves