If you're a regular listener of our podcast, you know that Paul and I enjoy baseball stats. Among all sports, baseball offers a uniquely large amount of data. And that has always led to an obsession with certain metrics. A good hitter hits .300, 40 home runs means you're a slugger, a great pitcher wins 20 games, and so on. Those stats are fun to follow. But in recent years, MLB's Statcast has shaken the baseball statistics world.
The "Statcast Era" began at the start of the 2015 season when MLB installed their high-tech cameras at all 30 parks. MLB defines Statcast as "a state-of-the-art tracking technology...capable of measuring previously unquantifiable aspects of the game." What are these unquantifiable aspects it's now measuring? For starters, exit velocity and launch angle for hitters and perceived velocity and spin rate for pitchers. The list of things Statcast measures is ever-growing, but two new items for 2017 caught our attention: Hit Probability and Catch Probability. Today, I'll cover Hit Probability. In the near future, I'll do a follow up post on Catch Probability.
So, what is Hit Probability? HP (not Harry Potter) is the percentage chance a batted ball will become a hit based on exit velocity and launch angle. Statcast can compare any batted ball against data from the Statcast Era (since 2015) and pump out a nice, clean percentage. This metric is helpful for evaluating hitters and pitchers. Both parties can only control so much. If a hitter hits the ball hard with a desirable launch angle, what else can he do? Similarly, if a pitcher draws weak contact, he is doing his job regardless of whether the defense helps him out. Let's see it in action. The following five plays are from the Cubs-Dodgers game on Thursday afternoon. The Hit Probability numbers come from Baseball Savant's game feed—a very cool resource.
What a bomb from Russell. And that bat flip... As you would expect, this one had a high Hit Probability. A ball hit that hard (110 mph) with that launch angle (27°) is a hit 98% of the time. This was the highest HP of the entire game.
Next up is Anthony Rizzo with another home run. As you can see, though, this ball wasn't hit as hard as Russell's (105.2 mph) and at a lower launch angle (21°). Hit probability: 82%.
This video contains two Albert Almora catches. Rough day for Corey Seager (and the Moonlight Graham fantasy team). These would be fun to look at with Catch Probability, but that will have to wait for another day. Here's a fun game: which hit had the higher Hit Probability?
I would have guessed the second because it looks more like a line drive, but it's actually the first:
Seager, 1st inning: 104.7 mph at 30° = 88% HP
Seager, 4th inning: 104.2 mph at 22° = 82% HP
Alright, the last example comes off the bat of Kyle Schwarber. MLB is stupid, so you'll have to click the picture to see the video. Schwarber hits a ball down the line that kicks off the glove of Scott Van Slyke for an RBI single. The ball was hit just 71.3 mph with a -16° launch angle. A ball hit like that is only a hit 6% of the time. It was the cheapest hit of the day across baseball and by far the cheapest hit all year from a Cub.