Brett Gardner continues to be the biggest beneficiary of the juiced ball

Something I like to do is revisit posts from seasons past and see whether the conclusions have held up over time. I’ve been writing on Pinstripe Alley for three years now, so there’s a decent enough sample size that some of my theses are right, and a good number are wrong.

After the Great Juiced Ball season of 2017, I wrote about how two Yankees, Didi Gregorius and Brett Gardner, owed a lot of their success to something being different about the ball. Didi’s improvement continued in 2018, when baseball reverted to a more conventional ball, but Gardner didn’t, having the worst offensive season since his first full campaign in 2009.

Flash forward to this year, and Gardner is having himself a heck of a start to the season. He has a 112 wRC+, is walking more than he strikes out, and has managed to stay off the injured list, which in and of itself is a victory for this team lately. He’s a notorious hot starter, falling off as the season goes on. As the evidence rolls in that the juiced ball is back, though, it’s time to consider how sustainable Gardner’s performance is going forward.

The 2017 and 2018 points here highlight how Gardner benefited from the juiced ball in the first place: his fly-ball rate held steady over the two seasons, but his ISO declined in year two. In 2019, both metrics are up, and he’s outperforming his xwOBA by 34 points, not to mention that he’s on a 30 HR/650 PA pace, which would be a career best if he maintained it. His career high sits at 21, set in the juiced ball season of 2017.

This is really the crux of the advantage of the juiced ball — players with marginal power benefit the most. Guys like Giancarlo Stanton and Aaron Judge have power no matter what ball they’re using. If a juiced ball adds 10 feet of flight to a batted ball uniformly, it just means that Judge is hitting that ball 430 feet instead of 420. For a player like Gardner, however, that extra 10 feet can be the difference between a ball in the seats and a ball dying on the warning track.

The difference between his wOBA and xwOBA is the key to projecting his future performance, and an indicator that the juiced ball is back. Based on his batted ball performance, Gardner should have a wOBA of .312, basically the same performance that Melky Cabrera is having. His actual wOBA so far this season is .346, the same as Mookie Betts and Jose Abreu. That delta between expected and actual wOBA is in the top quarter of baseball, and in a Normal Ball Era would indicate that Gardner’s performance would almost certainly regress.

But it’s not a Normal Ball Era, and that’s where things get funky. The juiced ball introduced a variable we can’t control for, since we don’t know what the ball will perform like in the next game. Gardner’s done everything right this season: he’s hit the ball in the air more than ever, and he’s increased his average exit velocity to the highest we’ve seen from him since Statcast started recording. He’s also cut down his strikeouts to a career-low rate, meaning he’s putting more balls in play overall, thus taking advantage of his better batted ball outcomes.

The strikeout rate thing probably isn’t going to last:

It’s just such a wild outlier — less than half his previous career-low —- that Gardner’s going to strike out a bit more going forward. That means that there will be fewer balls in play, and fewer positive outcomes driven by the juiced ball.

Still, the power stays tied to the ball, and as long as the ball is behaving in irrational ways, Gardner’s performance going forward should be better than you’d think. There’s a saying in investing that the market can stay irrational longer than you can stay solvent, and that’s kind of how I feel about Gardner. His performance shouldn’t be this good, but introducing a variable like the juiced ball might keep that weird performance going longer than we’d expect.