Before the debut of Statcast, public access to batted ball trajectories was generally limited to three subjectively classified groups—ground balls, line drives, and fly balls. A ground ball rate told the public how often a pitcher was generating ground balls, but didn’t say much about the quality of the ground ball allowed.
Not all ground balls are created the same. Table 1 shows batting average by ground ball launch angle, as measured by Statcast’s tracking system, which indicates a large improvement for pitcher outcomes the lower the launch angle on the ground ball.
|Launch angle||Batting average|
|5 to 0 degrees||.440|
|-1 to -5 degrees||.313|
|-6 to -10 degrees||.220|
|-11 to -15 degrees||.159|
|-16 to -20 degrees||.123|
|-21 to -25 degrees||.097|
|-25 degrees and under||.095|
It appears that by having a higher launch angle on a ground ball, the batted ball’s speed is maintained through the infield better than a low angle ground ball, allowing it to cut through defenses at a higher rate.
This is an example of a well struck ground ball with a launch angle of 7 degrees. It first touches ground a few feet in front of the third baseman, and despite a low exit velocity of 77 mph, the speed of the batted ball is maintained well enough through the infield to go for a hit.
This is the opposite end of the spectrum, a poorly struck ground ball with a launch angle of -31 degrees. The ball first touches ground just outside the batter’s box.
Before delving too deep into an individual’s numbers, it’s important to note that there are occasional problems with Statcast’s tracking system on both high-end (pop-ups) and low-end launch angles, with the system having problems tracking all launch angles on every batted ball. About 17% of all 2016 ground balls are missing an exact launch angle.
But of the batted balls that have been recorded, Jeurys Familia’s average launch angle of -18.1 degrees on ground balls is second-lowest in baseball among all pitchers who have thrown at least 750 pitches this year. The major league average launch angle on ground balls is -9.9 degrees.
In particular, Familia’s sinker generates an average launch angle of -20.1 degrees on ground balls, well above the MLB average of -11 degrees on ground balls off sinkers. With how filthy and electric Familia’s sinker generally is, it’s easy to see why that’s the case.
Familia’s 97 mph power sinker in the GIF above drops under the barrel of the bat, causing a very low launch angle of -24 degrees. The ground ball first touches the ground right in front of home plate.
Looking at launch angles alone on grounders can show a lot, because even high exit velocities that leave the bat at low angles can appear as weak contact to the eye because of how the ground slows the speed of the ball down as it makes its way through the infield.
Ground balls with an exit velocity of 100 mph have resulted in a batting average of about .440 on above-average—greater than -9.9 degree—ground ball launch angles. The same 100 mph exit speed on below-average—less than -9.9 degree—ground ball launch angles has dropped batting average down to about .210. It’s the same exit velocity off the bat, but the ground ball angle makes a large difference.