A Theory of Gary Sanchez: It's the Juiced Ball!

Gary Sanchez is a beast. Prior to Sunday's game, he had hit .400/.467/.900 in his first 21 games. He's already the top Yankee position player by WAR this season, which is all sorts of crazy. Sanchez was always a decent power hitter in the minors (He's consistently put up ISOs around .200, with 20-25 HR power). Even adjusting for any kind of hot streak this this represents, he's playing way above his pedigree. What the hell is happening?

Below, I'm going to lay out a theory. Here's the short version: the MLB ball is juiced, the MILB ball is not, and only certain types of hitters have been able to take advantage of the juiced ball. Gary Sanchez is one of those hitters.

Home runs rates are at all-time highs. Fangraphs Audio and Dave Cameron have a great summary of what is going on here. Basically, home runs rates began rising abruptly in the second half of the 2015 season, and the result can be attributed to a sudden rise in exit velocity, and is unlikely due to changes in weather, stadiums, players uppercutting the ball, the strike zone or an influx of new players. Ben Lindbergh and Rob Arthur don't find a ton of evidence from testing the balls, but note that the Triple-A home run rate has continued to fall even as the MLB rate has risen. The majors and minors both buy balls from Rawlings, but they are made in different factories

But, something else weird is happening. Home run rates are rising for the average MLB player, but not for the best home run hitters. No one is threatening the home run record, or coming even particularly close. Instead, a lot of guys who used to hit 10 home runs are now hitting 15, a bunch who hit 15 are now hitting 20, etc. The big hitch-swing guys haven't actually gotten better at all. To make this point mathematically, I'm going present some very simple statistics:

  • In 2014, the average qualified batter hit a home run in 2.6% of their PAs with a standard deviation of .15
  • In 2016, the average qualified hitter hit a home run in 3.6% of their PAs with a standard deviation of .15.

Put as simply as possible: A higher standard deviation in a sample means it has more variance. The highs are higher and the lowers are lower. Qualified MLB hitters are hitting home runs almost 40% more frequently, but the variance hasn't grown. This means the growth in HR rates comes from the middle hitting a lot more home runs.

A quick glance around the league reveals a ton of guys on track for 20+ home runs for the first time in their career. The Didi Gregorius' of the world are hitting the ball harder. In a world where exit velocity has increased, contact hitters become more valuable. Furthermore, the value of a line drive increases. Why? Because of the nonlinear relationship between launch angle and exit velocity. Hitters with an upper-cut launch angle don't benefit as much from increased exit velocity. So, add 2 mph to Mark Trumbo, and you get pretty much the same number of home runs.

But before we continue, let's take a look at Sanchez's launch angle chart:


Sanchez has an average exit velocity of 95 mph, which is pretty darn good, top-10 in the majors good. He's hot, so we should expect his small sample of exit velocity to be very high. The launch angles are more interesting. Sanchez isn't hitting anything at a high angle. No popups. He's locked into that 10-25 degree range. 

The average MLB exit velocity has increased about 1.4 mph since 2014, with a little more on non ground-balls. Let's call it roughly 2 mph, with a +/- 5 mph range. Below, I borrow a great graph from FiveThirtyEight, plotting batted balls by launch angle and exit velocity. I've very unscientifically sketched on Gary Sanchez's range of batted balls, and a rough guestimate of what it would look like centered on -2 mph:

Gary Sanchez's launch angle profile benefits more from a small increase in exit velocity than any other launch angle profile. Put differently: Sanchez's mean exit velocity is 95 mph, so let's call his range at 25 degrees 90-100. A large portion of that range (about 20% by my eye) falls into the home run range. Shift the box to the left by a little bit, and you very quickly get a lot of outs.

There's no doubt that Gary Sanchez is a hot hitter, but he's also built to capitalize perfectly on the juiced ball. He'll eventually start popping up more balls, and his exit velocity will come down a bit. But I think the power is here to stay. To explain why, let me start with Didi Gregorius' launch angle chart:

Like Sanchez, Gregorius doesn't pop the ball up too much. However, his whole profile is shifting a few degrees toward the ground, more in the 8-20 degree range for hits than Sanchez's 10-25 degree range. That profile is much less likely to hit home runs (even at similar exit velocities, and Gregorius is averages only 86 mph), although the harder balls will still go out. 

In my book, this is great news for Sanchez, assuming the ball stays juiced. His launch angle profile has become one of a power hitter with a higher BABIP, rather than a guy who flies out a lot with the occasional ball being hit hard enough for a home run. In the minors, his power was solid, but more limited.