An Overdue Barrel Rate Refresher

Before the 2020 season, I wrote a series of articles that looked at how much control batters and pitchers exerted over various outcomes: home runs, strikeouts and walks, fly balls, that kind of thing. I found the conclusions helpful, if mostly as expected: batters have more to say about home runs and line drives, but both sides have input on strikeouts, walks, grounders, and fly balls.

I decided to apply the same methodology – which I’ll detail below – to check on something that I thought I already knew the answer to: do pitchers exert any control over barrel rate, and how much do hitters do the same? Barrels are essentially batted balls hit extremely hard and at dangerous angles; I think they’re a great way of thinking about hard contact.

There’s already been plenty of research on the year-over-year stability of batter barrel rate. There’s been plenty on the fact that pitchers don’t do the same. Here’s a preview of my findings: I didn’t find anything that disputes that. I still think it’s useful confirmation, however, and I’m also pretty proud of the method. Thanks to Tom Tango, there’s even a rough rule of thumb to use if you want to estimate future barrel rates. Without further ado, let’s get to it.

The method in question works like so: first, take every batted ball from one season and calculate the barrel-per-batted-ball-event (Barrel%, let’s call it) for every pitcher and batter in the game. Next, divide them into quartiles with an equal number of batted ball events in each. For example, the quartile of pitchers that allowed the least loud contact gave up barrels on 3.3% of their batted balls. The quartiles that allowed the most checked in at 7.9% of batted balls. One minor note: I manually defined barrels for this exercise, which gave me slightly different barrel rates than Statcast (though within half a percentage point of batted balls overall).

That was just the setup. With every batter and pitcher tagged with a year-one quartile, I used the next year’s data to see how persistent barrel rates were. I tossed out pitchers hitting. Then, for every single batter, I separated their plate appearances into five groups: one for each quartile of pitcher, and one for pitchers who didn’t appear in the majors in the previous year. I tossed out the pitchers who didn’t appear in the majors; I don’t have a prior against them. Then, I looked at how each hitter did in terms of barrel rate against each quartile of pitchers. I did this using two years as Year One, 2016 and ’17, which let me avoid using either ’15 (when balls likely changed mid-season) or ’19 (when the coefficient of restitution in the balls may have changed, producing higher exit velocities) in my data set.

For example, in 2018 Mike Trout put 74 batted balls into play against the stingiest (lowest barrel rate) pitchers from ’17. He barreled up 12.2% of those batted balls. He put 83 balls into play against the next-best group (I’ll call them by their quadrants from here on out, so Quadrant 2) and barreled up 18.1% of them. He had 90 batted balls against Quadrant 3 pitchers – 11.1% barrel rate. Finally, he had 71 batted balls against Quadrant 4 pitchers and checked in at an 18.4% barrel rate.

I repeated this process for every hitter in baseball. I then weighted each by the lowest number of pitchers they faced in a quadrant – I didn’t want the data thrown off by Aaron Judge facing 130 pitchers in one quadrant and only 30 in another, or something of that nature. The results were clear. If the pitchers had repeated their Year One barrel rates, there would have been a huge spread between quadrants. Instead, there was almost none:

Pitchers displayed a wide range of barrel-suppressing numbers in Year One. In Year Two, the “hard-to-barrel” pitchers from Year One hardly performed better than their easy-to-crush counterparts.

On the other hand, batters who barreled up a lot of baseballs in Year One mostly did so again in Year Two. I repeated the same process for hitters; for each pitcher, I separated out their Year Two batted balls by batter barrel rate quadrant in Year One and threw out the batters who didn’t appear in the majors in Year One. The spread was meaningfully wider:

What does this mean? In simple terms, using this year-over-year quadrant methodology agrees with intuition and previous research: hitters supply the power, just like they supply the home runs. Whether a pitcher surrenders a ton of hard-hit balls in the air has a lot more to do with who they face than how they pitch. On the other hand, there isn’t zero pitcher impact; even equalizing across batters like we did, the low-barrel hitters from Year One allowed fewer barrels than average in Year Two.

That aforementioned Tango data twist? It gives us a rough estimation tool. Based on how far each group regressed to the mean in Year Two relative to Year One, we can estimate a “ballast amount” – how many league-average batted balls you should add to a player’s Year One barrel rate to predict Year Two barrel rate. For pitchers, it’s large – 131 plate appearances, to be exact. For batters, it’s tiny: 15 plate appearances. That’s because pitchers “regressed” 78% of the way back to average (in an average sample of 37 batted balls per quadrant) as opposed to only 33% regression on 30 batted balls per quadrant for hitters.

Why do this kind of study if I already knew the answer? Knowing the answer doesn’t mean it isn’t interesting to test it out another way, and I find this method to be intuitive. It helps me to think about what happens to the group of pitchers who were best at suppressing hard contact in one year and see how they did the next year. The same goes for hitters. Understanding what happens to the group as a whole makes it easier for me to think about how to treat individual hitters.

In any case, it’s great to see the same results no matter how you bake the pie. Does a hitter make plenty of loud contact? Believe it! Does a pitcher surrender barrels left and right? He might be doing something wrong – but you’d have to see a lot of hard contact to believe much of it. I suspect that a huge amount of the pitcher variation in barrel rate, in fact, comes down to the fact that you can’t barrel up a grounder, so groundball pitchers have an edge at barrel suppression. If you keep those two rules of thumb in your head, you’ll be a long way to understanding why pitchers focus so much on what they can control (walks, strikeouts) and hitters focus on what they can do best (pummel the ball into the stratosphere, at least until this year).