Clayton Kershaw’s Effect on the Dodgers Bullpen

Ken Rosenthal has an NL MVP vote this year, and the other day, he wrote about his thought process in regards to pitchers winning the award. He’d prefer to vote for a position player, but isn’t entirely against pitchers-as-MVPs, and he noted that a dominant starter who works deep into games doesn’t just affect the team on the day they pitch, as is commonly cited. Quoting from his column:

The one pro-Kershaw argument I do like – the one I recall making for Pedro Martinez in 1999 and 2000 – is that a dominant starting pitcher affects three games out of five. Kershaw averages more than 7 1/3 innings per start. Dodgers manager Don Mattingly can empty his bullpen the day before Kershaw pitches and manage a fully rested group the day after.

This does seem to be a potentially real benefit created by Kershaw that is not being accounted for anywhere in his own stat-line. While there is a lot of talk about players “making their teammates better”, this would be one actual place where it could exist, with a starting pitcher allowing his manager to reallocate his bullpen usage to the days around Kershaw, increasing their chances of winning on those days as well. This is the kind of thing that we wouldn’t capture by just looking at Kershaw’s performance.

But is it true? Rob Neyer was smart enough to realize that we should be able to find some data to test this theory, and so I bugged Jeff Zimmerman about it, and he was nice enough to query out the Dodgers’ bullpen usage on days before and after Kershaw pitched this season. Here are the results.

Game	Number of Relievers	Reliever Innings
Day Before	2.5	2.5
Day After	3.3	3.5
LAD Average	3.1	3.1
NL Average	3.0	3.0

There is definitely no effect on increased bullpen usage the day before Kershaw pitches, with the average number of relievers and reliever innings being well below both the league average and the Dodgers’ overall average for the season. On the day after Kershaw pitches, there is a small bump in reliever usage, but not anything that supports evidence of Don Mattingly “unloading the bullpen” after Kershaw allowed the group to rest. If you combine the numbers of day before/day after, the total average is 2.9 relievers and relief innings per game, a little below the average for both the Dodgers and the NL itself this year. In other words, the hypothetical effect hasn’t actually materialized this year.

But, of course, there are other factors in how many relievers pitch on a given day besides who is starting the next day, or how much rest the bullpen got the day before. For instance, how the starting pitcher that day is performing is going to have a much larger impact on the team’s bullpen usage. So let’s look at who has been pitching next to Kershaw all year, excluding the games in Japan, since those were under a different circumstance.

Starts the day before Clayton Kershaw:

Zack Greinke: 21
Roberto Hernandez: 3

Starts the day after Clayton Kershaw:

Dan Haren: 16
Hyun-Jin Ryu: 2
Roberto Hernandez: 2
Kevin Correia: 1
Carlos Frias: 1

And there’s the answer for why the Dodgers bullpen has worked less on the days before Kershaw takes the mound; he’s almost always been following Zack Greinke. Greinke regularly pitches into the seventh inning himself, and has gone at least five full innings in 28 of his 29 starts this year. The Dodgers haven’t pushed their relievers in the day before Kershaw starts, knowing he’d rest them the next day, because they just haven’t had to. Greinke’s presence as the day-before starter essentially wipes out any chance we’d have of finding a Kershaw effect on that day.

Haren, on the other hand, presents no such problem. He’s averaging 5.8 innings per start, below the NL average for a starting pitcher, and he has been chased before completing five full innings on five different occasions. And it’s not like Hernandez, Correia, or Frias are guys who pitch deep into games either, so the day-after Kershaw pitchers are basically a perfect opportunity for Mattingly to really use his bullpen, which has been saved by not only Kershaw the day before, but Greinke the day before that. On these days, the Dodgers have about as fresh of a bullpen as a team could possibly muster, and have used low-ish quality starters who don’t often work deep into games.

And yet, there’s basically still no visible effect. The Dodgers have used very slightly more the average number of relievers on days after Kershaw pitches, but that’s what we’d expect to find given the mix of pitchers pitching that day, no matter who had pitched the day before.

This doesn’t mean that Kershaw pitching deep into games doesn’t help the Dodgers in some way. After all, we know the Dodgers relievers are pitching pitching slightly more than the league average overall, so if they’re below the average on days Kershaw starts and below the average on the day before he starts, they have to be above the average on the other three days. Perhaps the effect of Kershaw resting his bullpen isn’t apparent the next day, but several days later, when pitchers are allowed to pitch for a second or third day in a row, when they would have otherwise needed an off-day if they had been forced to also work during Kershaw’s start.

This data does not prove that there is no added benefit from having a starter who works deeper into games, or that Kershaw isn’t adding value by giving his relievers extra rest on days he starts. It just isn’t obviously being reallocated into the days around Kershaw starts. It’s a nice theory that makes some sense, but unfortunately, the data doesn’t support the idea that Don Mattingly can manage differently around Kershaw’s games.