On Friday, I examined hitters with new plate approaches focusing on launch angle and plate discipline. I notice Brad Miller, Javier Baez, and Leonys Martin had each dropped their groundball rate but I didn’t have an idea of what is the ideal value. After spending way too much going down way too many paths this past weekend, the simple answer is average 20 degrees (32% GB%) with weak and/or fast hitters needing to push the value down to 15 degrees (42% GB%).
There is no need for readers to hang around any longer if they have more pressing matters like setting their daily or weekly lineups. For those looking for a little more explanation, thanks for staying around. I went through several methods I’m not going to discuss. I like simple useable answers and that’s what I’ll provide today.
The key to finding the idea average launch angle (LA) comes down to this graph in which our own Andrew Perpetua created.
The graph has basically two zones in which hitters want to maximize their exposure for the best wOBA. One is the dark red area in which MLB.com call Barrels. This area is where home runs live. The other region is the long orange region from 50 mph to 120 mph at ~15 degrees launch angle. These are line drives.
The next key is to create a range of a hitter’s normal batted ball outcomes. The standard deviation for exit velocity (EV) is 14 mph and for launch angles, it is 27 degrees. Here is the same graphic with the shaded area including one standard deviation in each direction from the oval’s center.
Hitters who average 85 mph or more exit velocity have the ability to reach the “Barrell”/home run region so they want to get their launch angle averaging around 20 degrees to maximize both their hits and home runs. The league’s best hitters who hit for both average and power live in this area like Mike Trout, Justin Turner, and Rhys Hoskins.
Not every hitter has the bat speed and control to lift every batted ball. It’s tough to hit a ball coming in at 95 mph. It may be impossible for some hitters to get the lift and continue to make acceptable contact. Some hitters have sold out for the extra lift (see Joey Gallo) and say screw contact. It’s a balancing act each hitter must work through.
Once a hitter’s average EV starts dropping under 85 mph, the barrel region gets further out of their reach. These are the hitters with warning track power and see their home runs dreams quickly die. These hitters need to drop their LA enough to live in the long orange finger collecting as many line drives as possible.
Knowing the launch angle needs to be around 20 degrees, I converted the launch angle to groundball rate (GB%). I like using GB% as a proxy for launch angle because GB% is available for minor leaguers and pre-2015 MLB seasons. Also, I found GB% to correlate better to LA because of the differences in classifying flyball, line drives, and popups.
Here are the conversion values.
Of the three original players in question, here they are with their groundball rates:
No matter their exit velocity, Miller and Martin likely need to lower their launch angle. Baez’s groundball rate is usable especially with an 89.1 mph average EV this season. His improvement is showing up with his .383 ISO but his .167 BABIP is dragging down his batting average.
Ideally, every hitter’s groundball rate is between 32% and 42% (15 to 20 degrees of launch angle) but for assorted reasons, some can’t or don’t achieve it. Some reasons are reasonable, others aren’t. With hitters trying to add lift, some may be taking their uppercut approach too far, especially considering their lack of raw power. Balance is the key.
Jeff, one of the authors of the fantasy baseball guide,The Process, writes for RotoGraphs, The Hardball Times, Rotowire, Baseball America, and BaseballHQ. He has been nominated for two SABR Analytics Research Award for Contemporary Analysis and won it in 2013 in tandem with Bill Petti. He has won three FSWA Awards including on for his MASH series. In his first two seasons in Tout Wars, he's won the H2H league and mixed auction league. Follow him on Twitter @jeffwzimmerman.