Does the Juiced Ball Lead to Straighter Pitches?

The ball is going faster in both directions these days. Velocities are up, exit velocities are up, and the players are openly discussing the changed nature of the ball. Slippery balls are maybe flattening out sliders this World Series. Are they, though? We can look at what’s happening now, and then we can also compare movement across different times in baseball’s rapidly changing environment as a comparison.

Turns out, movement is the product of a complicated relationship between the pitcher’s mechanics, the seams on the baseball, and how fast the ball is going. (Who would’ve guessed? Pitching is complicated.) Every ball is also slightly different — it’s put together by humans from the hide of a cow, after all — but we’ll never truly know exactly how different this World Series ball really is.

The faster a pitch flies, the straighter it should go, since it has less time to move. The tighter a ball is wound, the less drag it should have, and the straighter it should go, because there’s less air resistance pulling it in any specific direction. Baseball’s pitches have been flying faster with every given year, and the ball is presumably tighter. In other words, we can look at what’s already happened in the regular season — as the league has changed, rapidly, in the last three years — and see how that relates to what’s happening now.

If you’ve been reading these pages, you’re familiar with the evidence suggesting that the current ball is different than it has been in the past and that this fact has led to less drag and more home runs. Rob Arthur summed up his findings on actual, physical differences found in baseballs young and old:

Tiny variations in manufacturing can send the ball’s drag up or down seemingly at random. But small changes can still make a real difference between a ball slugged into the stands and one dropped into an outfielder’s glove. And the last three years appear to have featured a series of variations in the ball’s bounciness and air resistance that ended up causing the largest, fastest home run increase in history.

Less drag on the ball should also lead to less movement, a fact that has been difficult to research because of the change in tracking systems, from PITCHf/x to Trackman. But there might be some evidence the ball is flying straighter these days. Take a look at how movement has changed for right-handed starters during baseball’s regular season, between 2014 and 2017.

Balls are dropping much less these days, as you can see, but you might also notice that each pitch’s velocity has changed over this time frame. And velocity is related to movement. Alan Nathan once found that velocity and movement are negatively related when it comes to knuckleballs. I found an r-squared of .13 between curveball drop and velocity using all curveballs thrown in 2014, an example that mirrors changes exhibited by other pitches that year. Velocity matters, and more velocity generally means less drop.

Still, velocity is only one part of this, as the relatively low coefficient of determination indicates. Basically, curveball velocity explained 13% of the variance in curveball drop; the rest is mechanics and, well, the physical properties of the ball.

And already, we can see that there are confounding effects and results. Physicist David Kagan categorized the horizontal movement changes between 2014 and 2017 — you can see that many pitch types added horizontal movement, for some reason — as “contradictory data,” and it’s hard to argue with him. Why would reduced drag mean more horizontal movement? Shouldn’t reduced drag mean more drop? What is happening here?

We can probably hold mechanics out of the equation. Each pitcher is unique; it’s doubtful that all of them changed their mechanics the same way to affect movement. And besides, we’re looking at velocity and a possibly changing ball. We already have enough to deal with.

How about comparing movement and velocity from the pitchers in this World Series to their movement and velocity from earlier stages of this same postseason? Presumably, the adrenaline bounce the players feel in the postseason can’t get any more pronounced in the World Series? As Astros’ hitting coach Dave Hudgens said: “Oh, so now the games matter?”

We do see, generally, that velocity goes down as some fatigue creeps in. Changeups had been thrown 29 times in this series before last night’s game, our database says. That’s not a lot of changeups, and it’s not a lot of changeups upon which to base an opinion.

It’s possible that sliders are flatter in the postseason, but it’s not because they’re going faster. That difference in slider spin, collectively, isn’t significant. There’s certainly no pattern or statistically significant relationship between velocity and movement changes across pitch types here, if there was one above.

Another confounding factor looms, though: pitchers are human beings who can adjust to their own changing movement.

A well-placed pitch with less movement that arrives quicker might be preferable to the alternative. How well placed will that pitch be? Pitchers at the World Series were comfortable with the idea they might have straighter pitches right now, as they throw their hardest, but thought the adjustment to this newfound stuff was in the realm of their everyday job requirements.

“My slider velocity went up a bit,” Kenta Maeda admitted before describing the change in movement. “Maybe it’s a little smaller.” But nerves can affect you in different ways, as the bounced 50-foot curve can prove.

“You can overspin the ball, you can be a little too aggressive,” Rich Hill said. “It’s not a bad thing, though. It’s easier to adjust down than it is to adjust up.”

“I’m used to working in that range. It hasn’t been a big huge jump, it’s just been at the top of my velocity range,” reliever Brandon Morrow said. “You’re trying to really slow down so that things don’t get moving on you.”

“No,” answered Astros starter Justin Verlander when asked if he’s had any trouble adjusting to a difference in movement related to velocity. “I just focus on every single pitch in its individuality and try to execute it.”

“You notice when your command is a little better” thought the Astros’ Collin McHugh about game-to-game variation in movement. “Sometimes you know in the bullpen, and sometimes you get in the game, and you don’t know if you’re ever going to throw a strike.”

“When you get to this point — there are so many variations to your delivery and your repertoire over the season. Your body is changing, you may have some things, small injuries that are bothering you. When you get to this point in the season, it’s just about competing,” thought Charlie Morton. “You get what you have.”

Shoutout to the weather as a confounding factor, too. Cold weather changes the flight of the ball, and dry weather means the mud used to rub up the balls turns to “crumbly mumbly” as Rockies Director of Clubhouse Operations Allan Bossart put it. Drier mud means a slicker ball — and there’s no detailed set of instructions given to the people that mud balls up, meaning that it’s different in every park. Chaos. It’s enough to rethink the whole mud thing.

The ball is flying a little straighter as the ball gets harder, probably. But the ball is also flying faster, and that’s part of the equation. On top of that, we’re selecting for certain pitchers as we use these stats, and our pitchers are also adjusting their own pitches to be as successful as possible. Think of the in-demand high spin fastball pitcher, throwing higher in the zone.

It’s weird that the postseason slider is flatter without going faster, sure. But given how many variables come together to produce movement — velocity, release point, spin rate, grip, ball makeup, humidity, temperature, and the day-to-day nature of command — it’s not clear which part of the equation is to blame here.