Though it’s not entirely clear why, it nevertheless appears to be the case that the direction of a batted ball matters when you’re attempting to model the distance over which that same batted ball will travel. Perhaps it’s because of the “slice” balls exhibit off the bat. Perhaps it’s because they exhibit less slice when batted in the direction of the pull side. Perhaps the geometry of the field is somehow responsible for distorting the results. I don’t know. A physicist would be able to tell you more!

Anyway, direction matters, and so it looks like pulling the ball is good for power, even if you keep launch angle and exit velocity constant. And that’s relevant today because Michael Conforto is relevant today. With the return of Yoenis Cespedes to the Mets, the club has one outfielder too many. Both the Mets and their 29 hypothetical trade partners are probably wondering about Conforto’s future production. Which version of him is real: the one that raked in 2015 and September of 2016 or the one who hit 10% worse than league average for three-and-half-months this past season?

I already found earlier this month that Conforto’s “barreled” balls weren’t ideal — and perhaps that it was a result of having hit too many of them to center and left (i.e. the opposite) field.

But you hear coaches say that “pull power comes last,” that a player develops his ability to pull the ball later in the development process. In fact, Don Mattingly said almost that exact thing about Christian Yelich a few months ago to our August Fagerstrom.

From Fagerstrom’s post (bold is mine):

“I still think there’s room for him to grow,” Mattingly explained. “He still hasn’t really truly learned how to pull the ball. When he learns how to pull the ball, he’s going to be really scary. Because they’re not going to be able to do some of the things they do to get him out now when he finds that next angle. Once he gets that next piece in there, he’s going to be one of the best hitters in the game.”

So common wisdom suggests that pull power develops with age. Our data suggests that Conforto barreled too many balls to the opposite field. Is it possible that age will allow Conforto to barrel more balls to the pull side?

To answer the question, I asked Jeff Zimmerman to create aging curves for pull, center, and opposite-field percentages. The data is limited to what has happened since 2002, when we first got it from Baseball Info Solutions, but it produces a surprising result.

pullpercentageaging
Aging curve by Jeff Zimmerman using the Delta Method.

Based on the results here, it seems like the correct thing to say is that center-field power comes last. Batters add only a little bit of pull percentage over time, and nearly 10% of their opposite-field balls in play become center-field balls in play over the course of a long career. This isn’t to say that every player follows this path; it’s only to say that it’s the path that most players travel.

What this means for player development is complicated. If we’re looking purely at power, and not at defendability or on-base concerns — it is easier to defend a pull hitter, as Joey Votto has often pointed out — it looks like the ability to pull is fairly innate. You wouldn’t want to bet on a hitter to pull more going forward just based on natural development, at least.

But if power is not your only concern, and you would like a spray hitter who can cover more of the plate and hit pitches away as well as they hit pitches inside, maybe you want to see some opposite-field ability early on: the player is likely to only go to that field less often in the future.

Interestingly, the man who inspired this post is actually fairly average in terms of spray. The league’s average lefty pulled the ball 40% of the time and pushed the ball 26% of the time last year. Michael Conforto pulled the ball 42% of the time and pushed it 25% of the time, and will only add center-field balls in play if he follows the average trajectory. It’s possible he doesn’t add a ton of power going forward, at least not from pulling the ball more.

Conforto may add power, but it will come from the natural process of adding fly balls in place of ground balls. And for these other young hitters with opposite-field power, we’ll get to watch what happens to their power as they convert those oppo hits to center field hits, slowly.