The first season of Statcast™ is in the books, and we've learned a lot in a short period of time. Less than a year ago, terms like exit velocity, spin rate and perceived velocity were considerations only within small circles of hardcore fans or baseball insiders. Now those phrases and others like them are being seen in the everyday conversations of fans around the sport.
That's not to say the job is done, because it's not. We need to do better on providing context for what those numbers mean -- what, after all, is a 2,200 rpm curveball if you don't know if that's good or bad? -- and most of our successes have been with hitters and pitchers, which hasn't fed the hunger for improved defensive metrics. Those items haven't been forgotten, and we have a long offseason to attack them.
For now, let's focus on three big items that we learned from Statcast™'s debut season, things we maybe thought we knew inherently but could never put to numbers.
1. Pitch velocity doesn't lead to exit velocity
"Let the pitcher supply the power" is one of the oldest chestnuts in the baseball fan's arsenal, arguing that the more force with which a pitcher delivers the ball, the more force it will have coming off the bat. It's been repeated endless times on television broadcasts, and even the great Barry Bonds believed it to be true.
But now we can measure exit velocity, comparing it to pitch velocity, and the myth simply doesn't hold up. Roughly 15-20 percent of a batted ball's exit velocity is attributable to the pitch, which is to say, the batter is far more responsible than is the pitcher. You can easily see that on the exit velocity leaderboards, where the hardest-hit ball of the season was hit by Giancarlo Stanton at 120.2 mph off a 79.2 mph Mike Bolsinger pitch. Six of the top eight hardest-hit balls were delivered by the pitcher at under 90 mph, which makes sense -- no one's throwing hard in the Home Run Derby, right?
In fact, let's take the 1,000 hardest-hit balls of the season (all at 110 mph or above) and plot them based on pitch velocity, keeping in mind most pitches are thrown between 85 mph and 100 mph:
If that looks like a big mess where the two inputs have no relation to one another, well, that's the point. In the 87-mph range, there were 49 of the hardest-hit balls. In the 95-mph range, there were 47. Put another way, of the 639 pitchers who threw at least 100 pitches this year, the eighth-lowest exit velocity (83.55 mph) belonged to Aroldis Chapman, who throws so hard that we had to institute a "Chapman filter" to the pitch velocity leaderboards just to let anyone else show up.
2. Exit velocity can be used to track hitter health
Let's share another example. Washington first baseman Ryan Zimmerman was struggling badly through early June, hitting only .209/.265/.346 as he attempted to play through plantar fasciitis. He finally landed on the disabled list to rest the injury on June 11, and when he returned in late July, he hit .311/.372/.652 in 39 games before an oblique injury ended his season.
See if you can tell the difference in Zimmerman's exit velocity before and after the DL trip, indicated by the red line:
3. Spin rate can tell us a lot about fastballs
Of the 235 pitchers who threw at least 400 four-seam fastballs, Nathan Eovaldi's average pitch speed of 97.5 mph ranked eighth. But despite the heat, the pitch hasn't been that successful for him -- he allowed a .332 batting average and a .453 slugging percentage on it this year.
Why? In some part due to the fact that its spin of 2,140 rpm is neither particularly high nor low, and that's a lesson learned. There's not a great correlation between pitch speed and fastball spin; for example, Dellin Betances (97.5 mph) and Chris Young (87 mph) have nearly identical four-seam spin rates. But there is a good correlation between high-spin fastballs getting strikeouts and fly balls, and low-spin fastballs getting grounders.
That's how Young, for example, turned his low-speed fastball into a riddle hitters couldn't solve, and how Marco Estradadid the same thing. If you look at the five highest- and lowest-spin fastball pitchers, you'll see a pretty clear pattern. Ground-ball king Brett Anderson didn't miss many bats with his low-spin four-seamer; Jake Peavy, despite throwing slower than Anderson, got far more whiffs, thanks in part to high spin.
It's not that either high spin or low spin is better, it's that you want to be at an extreme on either end. Otherwise, your fastball is probably straight and hittable, as Eovaldi found. It's a problem he tried to solve by playing with a splitter, changing the grip on it to increase spin and velocity. After all, velocity is great, but a fastball that's straight, without any movement or deception? It's about the best thing a Major League hitter can see.
Mike Petriello is an analyst for MLB.com and the host of the Statcast podcast. This story was not subject to the approval of Major League Baseball or its clubs.