What's Eating Corey Kluber?

Corey Kluber has been one of my favorite pitchers since he burst onto the scene a few years ago. He doesn't have overpowering velocity, or a great fastball. Instead, he uses excellent command, a deep pitch repertoire, and one of the best breaking balls in baseball to succeed (his slider is great too). Or at least he did in 2014 and 2015. This year, things haven't gone well for Mr. Kluber.

As I write this on April 15 (his start on 4/17 is not included), he sits on a 4.85 ERA, backed up by a 4.73 FIP and 4.18 xFIP. His strikeout rate is down to 20% (basically average), his walk rate is up to 7.3%, which is still better than average but no longer elite, oh, and his fastball velocity is at a career low of 91.6 mph. Sure, it's early in the season and his home start against Boston was cold, but there are enough worrying signs here to dig deeper.

Get out your spade, put on your Red Wing boots, and start digging. First, he is at a career high HR/FB rate right now of 16.7%. That will almost certainly regress back to something closer to 10%. That only brings him down to his 4.18 xFIP, however, so there is much more here.

How about his swinging strike rate overall? Well, it's at a career-high 14.6%, so there's nothing wrong there. Is he getting behind in the count early? Nope, his first pitch strike rate is also at a career high of 69.1%. On top of that, hitters are actually making less contact than ever before, with a 69.7% contact rate. His out of zone swing rate is down 4% over last year, but that's not huge.

That 1 mph velocity drop I mentioned earlier hits all of his pitches about the same. He's throwing his slider 7% less than last season and his two-seam and four-seam fastballs are making up most of that difference with increased usage. Unfortunately, that doesn't really tell us much because those fastballs are actually doing better than ever for getting swings and misses this year.

We're about four feet underground at this point, time to dig a little deeper.

Here are heat maps showing where Kluber has pitched so far this season. First, his 2015 heat map, then the 2016 one.

Basically, he's throwing more low in the zone in that row of squares at the bottom, at the extreme low and inside for left-handed batters and inside to right-handed batters. All that pitching low has increased his ground ball rate, as you would expect (up 6% over last year). There isn't much else to note here.

How about his batted ball data? Well, I'm glad I asked. His hard-hit % has actually gone down 4% over last year, despite the poor results. There are two interesting things in his batted ball data, however. First, hitters are pulling the ball on him like never before, at a 46% clip. His previous high was 40%. Just a guess, but I imagine the reduced velocity leads to more hitters able to pull the ball against him. Second, he hasn't forced a pop-up yet this year. Those are basically automatic outs and his infield fly % last year was 7.8%, which was below the league average of 9.5%, but still something.

I have one last thing for show-and-tell here. This is a graph of his velocity over the last three seasons.

Note: shout out to the wonderful Fangraphs for these charts.

You can see that the last four starts of 2015 and the first two this year show similar poor fastball velocity. His Cy Young season over there in 2014 has him routinely in the 93-94 mph range. When he's down at 91, he's just not as dominant, like most pitchers. That extends to those last four starts in September and October, as well. His ERA in those was 4.15 with a 3.92 FIP. His HR/FB ratio was also at an elevated 15% in those starts.

Let's summarize all of this data. Kluber's been pitching poorly (really since September of last year). His strikeout "stuff" is as good as it has ever been. His walks are up a little, but it's not concerning. Hitters are pulling the ball more (40+% since September) and hitting more homers against him. His pitches are as deceptive as ever and seem to be very effective.

In the end, all we can say is that his velocity drop is the only real cause for his poor performance, as it allows hitters to pull the ball more and hit for more power. His poor K% is likely to bounce right back to normal, along with his walk rate. However, until his velocity returns to the 93 mph range, I'm not sure he can recapture his former success. At this lower velocity, he becomes just a very good pitcher, not an elite one.

Keep a close eye on that velocity as the weather warms up and he gets deeper into the season. If it doesn't show signs of improving, you might want to sell Kluber while he still has that ace shine on him. Tschus!