Dodgers' relievers dominant up in strike zone

Cubs slugger Kris Bryant noticed something about the dominant Dodgers relievers after they were swept in Los Angeles over the weekend. "Their bullpen," Bryant said to MLB.com's Ken Gurnick, "every pitch was right there at the top of the strike zone, every single one to all of us. It was unbelievable."   
Whether Bryant was expressing frustration or admiration -- perhaps both -- he is on to something, maybe more than he knew. The Dodgers' bullpen threw 12 scoreless innings (striking out 10) against the Cubs, they have by far the best bullpen in the National League, and a big part of it is exactly what Bryant pointed out. They're throwing the highest percentage of fastballs at the top of the strike zone of any bullpen in baseball, it's not even close, and it matters.
Here's what we mean by that. Let's exclude splitters from our definition of "fastballs," since they're supposed to dive, and let's look at the percentage of fastballs that are either in the upper third of the zone or just on the border. The Dodgers relievers have placed 12 percent of their fastballs in that zone; no other team has made it to even eight percent. The league average is below six percent. Texas is below four percent. It's a tremendous gap.

It's not just one pitcher skewing the results, either, because there's pretty clear evidence of this being a team-wide strategy. So far this year, 290 relievers have thrown at least 50 fastballs, and if we sort those pitchers by percentage of fastballs that went high in the zone, the Dodgers have the first name… and the second… and the third… and the seventh, 14th and 16th too.
Percentage of fastballs thrown high in zone in 2017 by relievers
36.5 percent -- Ross Stripling, Dodgers
36.5 percent -- Josh Fields, Dodgers
34.3 percent -- Chris Hatcher, Dodgers
34.2 percent -- Shawn Kelley, Nationals
31.4 percent -- Nick Goody, Indians
Pedro Báez (30.6 percent) is seventh; Grant Dayton (27.1 percent, 14th) and Kenley Jansen (26.1 percent, 16th) aren't far behind. Six of the top 16 relievers at throwing fastballs high in the strike zone are Dodgers, and while that's long been Fields' trademark, that simply can't be an accident otherwise.

The Dodgers, it's fair to note, did this more than anyone last year, too, but they've still taken the biggest step forward this year -- and do note that most teams are actually doing it less often. If there's a trend here, the Dodgers stand somewhat alone in doing it.

So the Dodgers' bullpen is throwing a lot of fastballs high in the strike zone. Is that meaningful? Let's explain why it is right now, starting with the fact that in the wake of the trend of hitters actively trying to elevate the ball for power, we actually expected that we'd perhaps see more teams try to throw high pitches, given that a generation of low-ball hitters might have trouble elevating those pitches.
It hasn't happened, not really. In 2016, we saw bullpens throwing 6.1 percent of their fastballs high in the zone. This year, that's 5.7 percent, meaning it's down. 
But there's evidence that if you can place those fastballs, you can really do some damage. The league average on those high fastballs is just .230, compared to .275 on middle-zone fastballs and .267 on low fastballs, and while conventional wisdom has long been that hitters will feast on those high fastballs if they're not placed well, the slugging percentage of .414 is better than .454 middle and comparable to .406 low. And the swinging strike rate high in the zone of 12.3 percent easily tops that of 6.5 percent middle and 4.8 percent low. You'll get fewer grounders, but you could get more strikeouts and lower averages -- if you can do it right.

The Dodgers, it seems, have managed to do it right, because on those high fastballs, they have allowed by far the the lowest amount of damage. Looking at Weighted On-Base Average (or wOBA; think on-base percentage but giving more credit for homers and extra base hits rather than treating all times on base the same) Los Angeles' bullpen has allowed a mark of just .217 on those high fastballs, where the league average is .306 and the last-ranked team, Washington, is at .498.
If you go back to the list of relievers that showed the Dodgers had six of the top 16 in terms of throwing fastballs high in the strike zone, you get some interesting stories. Sure, Jansen is an absolute stud, whiffing 34 without a walk allowed in 19 innings, and his success is more about movement than location.

But Stripling, for example, has turned himself from a low-upside back-end starter profile into an extremely valuable reliever, one who has struck out 33 in 28 1/3 innings so far with a 2.54 ERA, adding two miles per hour out of the bullpen and allowing the Dodgers the flexibility to not push Alex Wood or Kenta Maeda deep into games.
Fields (0.84 ERA, 26 K in 21 1/3 innings) was a little-noticed Deadline day pickup from Houston last summer; Hatcher (3.33 ERA, 31 K in 27 innings) is finally showing off the skills the Dodgers hoped to see when he came over in the Dee Gordon trade, doubling his high-zone fastball rate from 17.8 percent to 34.3 percent. Baez, for all the frustration over his slow pace, has whiffed 21 in 22 1/3 innings and has a stellar 1.21 ERA.
Interestingly enough, though Dayton shows up highly on this list, his high-zone fastball rate was actually down from 40.6 percent to 27.7 percent, and he's been unable to maintain his 2016 breakout success; he's spent much of May back in Triple-A.
It's not that everyone should suddenly throw high fastballs, of course. But if you have the right pitchers and the right approach, throwing high heat can really work. For the Dodgers, it's working -- they have a 21 2/3-inning relief scoreless streak -- and then some.