Starling Marte and BABIP: What Is It Good For?

The statistic that measures batting average on balls in play (BABIP) has become a popular metric for professional analysts - and everyday fantasy managers alike - when evaluating if a player can sustain his current batting average. A good rule of thumb for BABIP is that it usually reverts to a player’s career BABIP, as history has shown that, if a player has a very high BABIP, his batting average can be expected to drop (and vice versa if it’s a low BABIP).

The term “luck” is often thrown around when discussing BABIP, but if a player is hitting a ton of line drives, he is creating his own luck, as the league average BABIP on line drives so far this season is .642 according to Baseball-Reference. I find myself looking at BABIP (among many other stats) when trying to figure out why a player’s season is going one way or the other, and with half a season’s worth of data now available, trends are starting to develop.

This article in particular focuses on why the Pirates’ Starling Marte has one of baseball’s highest BABIP (.354) yet such a low batting average (BA). Of course, BABIP is just one stat and like any other individual stat, it should not be relied on solely when evaluating a player.

Currently, there are 21 hitters with a BABIP of .350 or better (for reference, there were 16 such hitters in 2013). Of these 21 hitters, Starling Marte has the lowest batting average, hitting just .259. Last season, Marte hit .280 in 135 games. So what’s the reason for his lower batting average, especially considering he has a high BABIP? Spoiler alert: It's not because he's losing playing time to Josh Harrison or Gregory Polanco.

One major difference immediately stands out between this season and last. Marte’s strikeout percentage (K%) has increased by just over three percent - his 84 strikeouts are the 15th most in all of baseball. Marte whiffed 138 times in 135 games last year, so striking out a lot is nothing new for him. But he’s doing it even more frequently this season. Note that striking out harms batting average without affecting BABIP, since, obviously, when a batter strikes out, he fails to put the ball in play.

The next thing I noticed about Marte is that his ground-ball percentage (GB%) has gone up by 4.3% from last year, which I initially thought was the problem. But upon further review, I’m not sure that it is.

When I saw that Marte’s GB% had gone up significantly, I assumed that meant that his line-drive percentage (LD%) had gone down, but it’s actually exactly the same as it was last season (21.6%). This means that the change came in the amount of fly balls he’s hitting, which is down the same 4.3% that his GB% has gone up. Remember how I mentioned that the league average BABIP on line drives this year is .642? Well, for ground balls, the average is .243, and for fly balls it’s .082. In other words, a batter’s chances of getting a hit are much greater when he puts it on the ground as opposed to hitting a fly ball.

Ok, so Marte is hitting more ground balls and less fly balls, meaning his batting average should be higher than it was last year, right? But not so fast.

The SIERA page on FanGraphs mentions that "ground balls go for hits more often than fly balls (although they don’t result in extra base hits as often). But the higher a pitcher’s ground-ball rate, the easier it is for his defense to turn those ground balls into outs. In other words, a pitcher with a 55% ground-ball rate will have a lower BABIP on grounders than a pitcher with a 45% ground-ball rate." I’d argue that the same is true for batters who hit a large percentage of ground balls, and therein lies the problem with Marte.

Basically what the quote above means is that, even though batters have a BABIP of .243 on grounders versus .082 on fly balls this season, it doesn’t automatically mean that hitting more grounders (compared to fly balls) equates to more hits. There are only 12 hitters in baseball with a higher GB% than Marte’s 55.1%. Their average BABIP is .310 and their average batting average is .266, and not a single hitter is batting over .292. Based on league averages, they have a better chance of getting a hit when hitting a grounder as opposed to a fly ball.

But this holds only to a point, as hitting too many grounders will become counter-productive. The .044 difference in BABIP to batting average for these top-12 hitters (.310 to .266) is roughly the same difference in BABIP to BA for the top-12 hitters in terms of fly ball percentage (FB%), at .038. While this is a small sample size, the batting average of a dominant fly-ball hitter proves to be more accurate to his BABIP when compared to a predominantly ground ball hitter, in spite of the high difference in the league average BABIP of the two. This means that my initial thought about Marte’s increased GB% hurting his overall batting average is likely true.

Another potential reason for Marte’s low BA compared to his high BABIP is his batting average on hard-hit balls. According to Mark Simon, who works for ESPN’s stats and info blog, Marte has the 16th-worst batting average (.609) on hard-hit balls. Unfortunately, data on hard-hit balls is not publicly available online, so I don’t have anything to compare this to. As you can guess, hard-hit balls tend to go for hits quite often. I’m not sure that being on this list is anything other than bad luck, but it could be another reason for Marte’s low overall batting average.

Last season, Marte was a speedster (41 stolen bases) with some pop – his .161 Isolated Power (ISO) ranked 70th overall – who also struck out a lot. This season, the speed is still there (18 stolen bases), but his ISO has gone down to .126 - likely due to his increase in GB% and decrease in FB% - and he’s striking out more. Even though Marte is fast and can turn grounders into hits (he has the sixth-most infield hits this season), he's doing more harm than good by hitting more ground balls this year and his numbers – and not just his batting average – are suffering because of it, even with baseball’s 15th-best BABIP.