Craig Kimbrel should not be the Cubs closer

As many of you know, my second favorite team is the Boston Red Sox. I was lucky enough to see them play a lot of baseball when I lived in Boston from 2007-14, which was basically a golden age of Red Sox baseball. I kept watching after I moved to Chicago and as a result, I’ve watched a lot of Craig Kimbrel over the years. When he is right he is one of the most devastating relievers in the game and many people believe he’s already put together a Hall of Fame-worthy resume. The thing is, he is not right at the moment and until he is he should no longer enter Cubs games in save situations.

In his career Craig Kimbrel has been a strikeout machine. His career K/9 is 14.58. He has struck out 899 batters across 555 innings. His career BB/9 is 3.58, which isn’t outstanding, but it’s never been a huge issue given the strikeout numbers. Over the course of his career he’s also very effectively limited the long ball with a HR/9 rate of 0.75 and a HR/FB rate of 11.3 percent.

Kimbrel has built this impressive record mainly on two pitches. He has a fourseam fastball that averages around 96 miles per hour. He combines that pitch with a knuckle-curveball that averages 85.5 miles per hour. Over his career both pitches have generated a ton of swing and miss due to their movement. In fact, this is his intro for Brooks Baseball Pitchf/x tool (emphasis mine):

Craig Kimbrel has thrown 9,996 pitches that have been tracked by the PITCHf/x system between 2009 and 2020, including pitches thrown in the MLB Regular Season, the MLB Postseason, The World Baseball Classic, Spring Training and Fall/Winter Ball. In 2020, he has relied primarily on his Fourseam Fastball (96mph) and Curve using a Knuckle Curve grip (86mph).

His fourseam fastball generates a high number of swings & misses compared to other pitchers’ fourseamers, generates a very high amount of groundballs compared to other pitchers’ fourseamers, has some natural sinking action, has well above average velo and has slight armside run. His curve is thrown extremely hard, generates an extremely high number of swings & misses compared to other pitchers’ curves, results in more flyballs compared to other pitchers’ curves and has slight glove-side movement.

I can sum up Craig Kimbrel’s current problems in Chicago in one table:

During his time in Chicago Kimbrel’s walk rate and HR rate have skyrocketed while the bottom has fallen out of his K-rate in 2020. I can already hear someone screaming “Small Sample Size” in the comments, so before you put me on blast for judging a future Hall of Famer on 1.2 innings I want to show you this stunning data from Statcast: Kimbrel has thrown 23 curveballs in 2020 and has not generated a swing and miss on ANY of them:

It isn’t just that batters aren’t swinging and missing on his curve. They aren’t swinging at the pitch at all. The closest thing that Kimbrel has generated to a swing on his curveball was this check swing from Franchy Cordero last night:

MLB | Marquee Sports Network

In 2020 Kimbrel has faced 15 batters with these results:

That is a big load of Y I K E S.

But there is more. Since batters clearly seem to be recognizing Kimbrel’s curveball they are able to just sit on his only other pitch — a fourseam fastball that has averaged right around 96.4 MPH in 2020. That pitch used to generate a lot of ground balls, now it generates a lot of hard contact, and, you guessed it — home runs. Here are the exit velocities on balls in play for Kimbrel in 2020:

I do not think Kimbrel is irrevocably broken. The velocity is still there, but something mechanical is clearly off. I’m not sure whether he is tipping his pitches with his delivery or if the slightly larger gap in spin rate between his fourseamer and curveball are just making a big enough difference that players can recognize those pitches better now.

At the end of the day, it really doesn’t matter. It seems pretty clear that batters know what is coming from Kimbrel right now, and they are just mashing those fastballs. Until batters start offering at his curveball again it’s a huge gamble to put him in the game, let alone a save situation.