Maybe it’s gone unnoticed, but Craig Kimbrel hasn’t been himself lately.

In his most recent appearance on Saturday, he served up a home run to Orioles’ outfielder Trey Mancini on a 97 MPH fastball.  It was the second home run he’s allowed this month, and the seventh he’s allowed this year.

The 30-year-old Red Sox closer has struggled with command all season long.  He’s lost velocity on his fastball.  He’s walked a career-high number of batters.  Since June 22nd, he’s only pitched three clean innings.  He’s dealing with issues that he’s never dealt with before.

More recently, he’s gone on a skid.  In his last six appearances, he’s allowed five runs total.  For comparison, 37 of his previous 42 appearances were scoreless.

The Red Sox chose not to acquire any bullpen help.  But next to the Yankees and Astros, their relievers don’t match up.  They need Kimbrel to perform.  Lately, he hasn’t.

So what’s gone wrong?

There’s no way to argue that he’s been “bad” or “below-average” this season, or even mediocre by any stretch.  He’s still the most talented reliever in the Red Sox bullpen, and among the top relievers in baseball.  It’s not that he’s lost his craft.  He’s still a dominant closer, and he’s maintained that status since he entered the league eight years ago.

Statistically, Kimbrel has only been a slightly-less-elite version of himself.  To give you an idea, among 131 relievers with at least 40 innings pitched, he ranks 14th in fastball velocity (96.9 MPH) and 2nd in curveball velocity (86.4 MPH).  He ranks 5th in swinging-strike percentage (17%).  He’s generated a 2.63 ERA and a 3.04 xFIP.  Those are all excellent numbers that match his excellent career numbers.

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But Kimbrel has been far from excellent lately.  In his last six appearances, he’s only managed to keep runs off the board once.  Of 144 pitches, just 54% were strikes.  Batters have slashed .250/.419/.625 with a 1.044 OPS.  His ERA is 7.11 over that six-game stretch.  He’s allowed 2 home runs and 7 walks to 31 total batters.

In August alone, he’s allowed a 6.75 ERA, his worst month of this season by almost three full points.

Those numbers are unprecedented for the closer, who’s never been an issue until now for the Red Sox.

So, what’s wrong with Kimbrel?

1. He’s not throwing as hard

It might not seem like much, but 1-2 miles per hour in velocity can be a massive difference for opposing hitters.  That’s the difference in speed Kimbrel lost this season on his fastball.

velo by season.png

While his curveball is virtually unchanged, his fastball velocity has dropped by almost 2 MPH.  For a two-pitch closer, who relies so heavily on the effectiveness of his heater, it makes sense that he’s suffered the consequences of that 2-MPH drop.

It’s even more alarming when you look at his fastball and curveball combined.

all pitches velo by season.png

For most pitchers, losing velocity causes two things to happen:  (1) more batters can get their bats around on the ball to make contact and (2) more batters hit home runs.

Kimbrel is no exception: all but one of the seven home runs he’s allowed this year have come on 97-MPH fastballs in the middle-middle part of the strike zone.

While a 99 MPH fastball had enough speed to blow by opposing batters so that they couldn’t square up on the ball, a 96 or 97 MPH isn’t fast enough.  More guys can catch up to 96 MPH and barrel it over the fence.

This concept is amplified when Kimbrel faces left-handed hitters.  This season, lefties have slugged 1.400 against him on middle-middle pitches.  Prior to this season, they slugged just .414 in the same zone.

iso vs left.PNG

What’s to blame for this drop in velocity?  There’s not much of a case to be made other than purely his age.  Thirty is around the time most pitchers begin to show their wear and tear physically, and Kimbrel turns 31 next May.

He could be fatigued or worn out, although he hasn’t thrown an excessive amount of innings this season.  It could be something like cooler weather or purely a fluke.  But the evidence points to a velocity loss caused by age, which means Kimbrel needs to start reworking his pitch mix and locate his strike zone more effectively.

2. He’s not getting batters to swing-and-miss

The essence of Kimbrel’s game is the swinging strikeout.  Without getting guys to whiff, he’s not going to have much success.  And while he’s still been a top strikeout reliever in baseball, he’s also struck out far fewer batters than last season.

K% by season.png

Kimbrel has struggled to make batters miss in 2018 because of a career-low strikeout percentage on his curveball, at just 41%.  Batters have swung-and-missed at his curveball just 18.3% of the time this season – another career-low.


Another issue is that he can’t locate his curveball, and when he does, batters don’t whiff as much as they used to. 

This type of dramatic change suggests that he might even be tipping his pitches.

Even worse, when batters do manage to make contact on his curveball, they’re hitting it harder and in the air.  This season, the average launch angle on balls-in-play from his curveball is 11 degrees, his first positive number recorded in the StatCast era and a career-high by 12 degrees.  (-3 in 2017, -1 in ’16, -6 in ’15)

Because the Red Sox have been winning games at such a torrid pace, Kimbrel’s struggles have been mostly passed over.  But it’s tough to ignore that he’s struggled recently, even when the best lineup in baseball can bail him out.

This winter, the Red Sox will decide whether to pay him for his future performance.  It won’t be as easy of a decision as most thought entering this season.  They need to decide if his last few weeks are an anomaly or the start of a real trend.

Either way, his issues are definitely troubling for the Red Sox, who already have a shaky bullpen for a championship contender.

Kimbrel still has seven weeks left until the playoffs.  That leaves him plenty of time to iron out any mechanical problems that he’s been struggling with.  Given his track record, the Red Sox shouldn’t be worried.  In the end, it all comes down to his performance in October.  If he can pitch well when it matters most, his most recent skid will be all but forgotten.

Ben Healey is a high school senior from Nottingham, New Hampshire.  You can contact him on Twitter here or email here.

  • Image credit to The Boston Globe
  • All statistics credit to BaseballSavant, BrooksBaseball, and Baseball-Reference

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