# What exactly do launch angles mean, anyway?

Given how new Statcast is, I’m sure just about everyone has wondered what exactly launch angles mean. During games you see numbers flying through the game feed. So and so hit the ball 98mph at 27 degrees! Someone else hit it 101 mph at 37 degrees, or 5, or 17! Woo hoo! But what does this stuff mean? It’s hard enough to visualize what a 17 degree angle might look like, let alone what it means during a baseball game.  You may have heard something along the lines of “a launch angle in the high 20’s, 27-29 degrees, will maximize distance,” and that means more homers, right? So maybe hitting the ball on that angle, as hard as you can, is the best way to provide as much offense as possible.  However, only thinking about maximizing distance makes me a little uncomfortable. It feels, dare I say, a little old school. We live in a new era with new data to play with, and, hey look, I’ve made some charts!

Alrighty, first off, I’m using four main stats here. First, vertical launch angle, which I’m getting from Baseball Savant. Second, xBACON, expected batting average on contact. Third, xOBA, expected on base average. xBACON and xOBA are both calculated using a balls exit velocity and launch angle, which you can read about here. Finally, % BIP, percent of balls in play. It may be worth nothing, when referring to league wide stats, xOBA and wOBA are the same, as are xBACON and BACON, I’ll be saying xOBA and xBACON referring to league stats for the sake of consistency.

In this first chart you’ll see league average xBACON, xOBA, and % BIP. One thing you should notice right away, xBACON and xOBA peak in two different places. xBACON peaks around 12-13 degrees, which makes sense, those are going to be your hard hit line drives. They don’t have enough of a belly under them to allow a fielder to run under the ball before it lands, but they also aren’t so low that they hit the ground and slow down. As the angle goes up beyond 14 degrees, xBACON rapidly falls off, falling from .710 at 12 degrees down to .386 at 30 degrees, which comes out to about 18 points off your BACON for every degree you hit the ball over 12 degrees. From 30 degrees to 40 degrees it drops from .386 to .127, which is about 25 points off your BACON for every degree of change above 30 degrees.

xOBA peaks around 24-25 degrees at .737. It is worth noting that MLB defines a fly ball as any ball hit above 25 degrees, so xOBA peaks just below the fly ball threshold. xOBA ramps up with value along with xBACON, before diverging around 14 degrees. xOBA then increases in value slowly until 25 degrees, then drops off pretty rapidly, falling from a peak of .737 at 25 degrees to .193 at 40 degrees, which is about 36 points off xOBA for every degree above 25 degrees.

Balls hit between -3 and 36 degrees have average or better xOBA, and balls hit between -3 and 31 degrees have average or better xBACON.

I can add in a few ballparks to show how things differ from one area to another. For example, you can see how Colorado has both a higher xBACON peak around 12 degrees and a second local peak around 26 degrees. The increased peak around 12 degrees is no doubt caused by its huge outfield, particularly short line drives that land between second base and the center fielder, while the increased peak around 26 degrees is likely the result of the thin air allowing more fly balls to leave the park as dingers. On the flip side, Oakland has a much reduced peak around 12 degrees, .651, 59 points below league average.

You can feel free to play around with these charts, I’ve put them in a google doc where you can select 3 parks, 5 batters, and 5 pitchers and compare their xBACON, xOBA, and % BIP however you’d like.

#### Two bonus Google docs full of charts!

I was curious how pitch zone might effect batted ball quality. Baseball Savant has some of this data readily available, but I wanted to include xOBA and xBACON, as well as vertical and horizontal launch angles. I’ve also included a stat I haven’t spoken much about yet, Value Hits. This is my Statcast based measure for “Hard Hit”. Value Hits are not defined by velocity or angle, but rather by the xOBA value of the batted ball, the weighted value of the ball given its odds of being a single, double, etc. Any ball with a value over .88, roughly the value of a single, is a Value Hit (VH). You can select a batter, all batters, all lefties, or all righties and view how their stats break down by zone.

Perhaps less useful, I made these charts to compare the spin rate of pitched balls to xOBA. I created this more as a curiosity than anything else, I don’t know if it is useful. You can pick up to 10 pitchers along with one of their pitches, and see how its spin rate correlates to batted ball value. For example, Matt Harvey has a roughly linear relationship between slider spin and batted ball quality. Lower spin = harder hit balls. Not every pitcher has this relationship. For example, here you can see Matt Harvey and Jake Arrieta.

Jake Arrieta’s slider definitely gets better with higher spin, but nowhere to the same extent as Harvey. Which is especially troubling as Harvey has lost a good deal of spin on his slider. That doesn’t bode well. Again, you can feel free to play with this Google doc.

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Andrew Perpetua is the creator of CitiFieldHR.com and xStats.org, and plays around with Statcast data for fun. Follow him on Twitter @AndrewPerpetua.

Member
minisidd

Thank you for the charts, and your thoughts! I really enjoyed this article. I’m actually pretty interested in the spin rate/ quality contact correlation. The charts confirm mostly what you’d think since a higher spin rate means more movement means it’s tougher to square up. I’m actually more curious about how spin rate effects balls that are squared up. Do line drives die out faster if the pitch has a forward spin rate (curve) as opposed to a backwards one (Fastball?) Or is that a non-starter since the spin is reset once contact is made?

I suppose that kind of specific question will have to wait until more data comes in… Looking forward to ever more enlightening horizons. Also xBACON is my new favorite name for a baseball stat.