Kopech is on fire. Stats show he's even better

April 27th, 2021

Remember how good was supposed to be when he first came up? Well, he's that good now.

Three seasons after Tommy John surgery derailed his MLB debut, the 24-year-old White Sox flamethrower is pitching up to his status as Chicago's No. 2 prospect and MLB's No. 34 overall. Whenever you face him -- as a starter, or out of the bullpen -- he's going to strike you out. Kopech had 13 K's in his first 7 2/3 innings of the season as a reliever, then jumped into the White Sox rotation for the first time since 2018 and just struck out 10 in five innings in his second start back.

That brings Kopech to 27 K's in 15 2/3 innings for the season -- 15.5 per nine innings. He's running a 1.72 ERA in six appearances. And the Statcast data says he's more than for real.

Lowest expected ERA, 2021
Minimum 50 batters faced

  1. Corbin Burnes (MIL): 1.15
  2. Jacob deGrom (NYM): 1.33
  3. Michael Kopech (CWS): 1.38
  4. Jonathan Loaisiga (NYY): 1.63
  5. Gerrit Cole (NYY): 1.65

xERA: Based on quality of contact allowed, walks and strikeouts

The only two pitchers ahead of Kopech are literally setting MLB records for dominance -- Burnes' 49 strikeouts without a single walk to start the season are a record for a starting pitcher, and deGrom's 50 strikeouts through four starts are a record, too.

Kopech has been extremely dominant, too. He's striking out 47% of the batters he's facing, behind only deGrom. His return to the White Sox has been worth the wait. Here's why he's so good right now.

The power fastball

Kopech's fastball is explosive in two directions: it rides, and it runs.

He has both the high velocity to throw a prototypical power fastball, and the high spin rate to throw a prototypical "rising" fastball. Kopech is averaging 96.3 mph on his four-seamer this season and 2,550 rpm, while the Major League average is around 2,300 rpm.

What's just as important is that he spins the ball efficiently. Kopech has an active spin percentage of 96% on his fastball. That means nearly all of the spin on his four-seamer contributes to the actual movement on the pitch.

Kopech's fastball only drops 11 inches from his hand to the plate. That gives him about two inches of "rise" above average. His fastball also gets about 12 inches of arm-side run -- nearly four inches above average in horizontal break.

In other words: the efficient spin is actually making Kopech's fastball carry through the strike zone, which is what makes it a swing-and-miss fastball, especially when Kopech elevates, which he does well over half the time. With his combination of stuff and the way he attacks, hitters are whiffing on over a third of their swings against Kopech's four-seamer, giving him one of the highest fastball swing-and-miss rates in the league.

The results speak for themselves. Opponents are batting .063 in plate appearances ending on Kopech's four-seamer, and they've struck out in over half of those. They're 2-for-32 with 18 K's.

The wipeout slider

Kopech has sharpened up his slider from his rookie season to now. Look at the difference in the metrics:

Kopech's slider, 2018 vs. 2021
Velocity: 82.8 mph to 85.0 mph
Spin rate: 2,310 rpm to 2,449 rpm
Vertical drop: 41.3 inches to 36.5 inches
Horizontal break: 7.9 inches to 6.7 inches

He's throwing his slider harder, and with tighter break. Why would that help? It brings the slider a little closer to his fastball -- the pitch he's most likely to sequence it with -- and differentiates it a little more from his loopier curveball, so that both his breaking pitches don't blend together.

Here's how Kopech's fastball-slider-curveball trio profiled in 2018 compared to now in terms of velocity and spin.

Fastball: 95.4 mph / 2,559 rpm
Slider: 82.8 mph / 2,310 rpm
Curveball: 78.2 mph / 2,254 rpm

Fastball: 96.3 mph / 2,550 rpm
Slider: 85.0 mph / 2,449 rpm
Curveball: 79.5 mph / 2,480 rpm

The spin on all three pitches is a lot more similar in 2021, while the velocity differential between all three is a little more balanced.

In 2018, Kopech's four-seamer was 12.6 mph faster than his slider, and his slider was only 4.6 mph faster than his curveball, and none of the three pitches spun the same way. In 2021, his slider is about a mile per hour closer to his fastball and about a mile per hour farther from his curveball, and all three have the same amount of spin. But they break in three different directions.

No wonder nobody is squaring up Kopech right now. Barely half the hitters who face him are putting the ball in play to begin with, and even when they do they aren't driving it with any authority. Only one of the 27 batted balls against him this season has been both hard-hit (95+ mph exit velocity) and in the launch angle sweet spot (8-32 degrees). He's almost eliminated opposing hitters' ability to do damage against him.

It feels like ages ago that Kopech was blowing away now-teammate Yoán Moncada with triple-digit heat in the 2017 Futures Game. But that same electric arm is in the big leagues today, and it's about time.