Double Plus: Nick Ahmed’s Platoon Splits Were as Bad as You Thought

Just being perfectly honest, you don’t really need to read this post. If you’ve seen the headline, you know all you need to know. It was fun, though, to use batted ball velocity data to pick apart David Peralta‘s better success against lefties in 2015, and I think enough of that to rely on it to figure out some other things.

Ahmed’s fate against right-handed pitchers in 2015 was about as terrible as his defense was fantastic. Since he was worth about 15 runs on defense over and above the average fielding of a major league shortstop, that’s really saying something. According to the splits at FanGraphs, though, he really was about 17 runs worse on offense than the average hitter (not shortstop) in 2015 against RHP (-16.8 wRAA). One reason he still managed a 1.7 fWAR last year was that his defense at that position really was that valuable, but also because when Ahmed faced LHP, he did quite a bit better (3.1 wRAA in less than half of his plate appearances overall, but who’s counting).

We tend to use weighted Runs Created Plus in these parts, though, so lets’ do that, measuring Ahmed and his alter ego against the league average for creating runs by non-pitchers (set at 100). Ahmed’s 115 wRC+ against LHP was short of the offense generated by guys like Peralta and A.J. Pollock, but still in “hey, this guy’s pretty good” territory — think Welington Castillo and his overall wRC+ of 116. Ahmed’s 50 wRC+ against RHP was, well… Chris Owings in 2015, either at or close to “please make it stop” territory.

Still, until this last year, we might have looked at Ahmed’s BABIPs and concluded he was burned by bad luck. Where a league average BABIP is around .300, and it’s not that normal to see deviations of 3o or more points off of that, Ahmed looks extremely unlucky against RHP (.231 BABIP) and fairly lucky against LHP (.326 BABIP).

The bad news and the good news is that those statements probably aren’t true. Batted ball velocity makes an enormous difference in results; balls hit in the very high 90s and 100s in terms of mph tend to become hits about 70% of the time, and then it’s a narrow band of “okay cool” in the mid 90s with 35% hits or so… and then 20%-25% for everything else. No hard hits, and you look terrible. Lots of hard hits, and you look like Peralta or Jake Lamb or maybe a lot like Howie Kendrick.

We’re not dealing with a tremendous sample size here, especially with Ahmed’s batted balls versus lefties — he only had 94 of those in 2015. He never quite hit that 106 mph threshold against a lefty, although he did manage a 106 mph single against a righty in April, following that up with a 107 mph one-base blast in September. Still, look at the huge difference here in the difference in dark gray, a good indication that looking only at the data with velo reported should only be done with caveats. Many of those unreported hits tend to be weakly-hit balls (but not all), and weakly-hit balls turn into hits only barely more than never.

I guess, then, Ahmed may actually have been just a bit lucky in 2015 when facing lefties — by rights, maybe he got one or maybe two hits that we might not have expected. The batted ball profile is worlds apart, though, really probably establishing that the platoon split isn’t going away any time soon. Assuming we get the same data in 2016, we’ll be looking to see if Ahmed is hitting the ball with a little more authority a little more often — if that doesn’t start to happen by midseason, the D-backs may end up moving to a strict platoon, once they can find a partner.