Why doesn’t Chris Stratton throw his curve more often?

To send the Astros to the 2017 World Series, which the Dodgers lost in case you forgot, Lance McCullers Jr. threw twenty-four straight curveballs against six different batters retiring all of them. McCullers’ curve is easily his best pitch, but still, it was unprecedented for him or any pitcher to lean so heavily on a breaking ball.

Even Sergio Romo regularly mixes in his two-seamer, which he used to get the final out of the 2012 World Series, which the Giants won.

To someone who’s never watched baseball, McCullers’ strategy to rely heavily on his best pitch. If you have an amazing curveball, throw it. Why mess with basic attacks if you can use Knights of the Round every time?

But Mike Krukow often talks about how the fastball is any pitcher’s best pitch, how all secondary pitches exist to make the fastball better, how mixing speeds is the key to success.

It’s not just Krukow either. Greg Maddux talked about how he wanted his pitches to look like “a column of milk,” or that they all look the same until they reach a certain point and split away. Baseball Prospectus’ tunneling information is predicated on the idea that the sequencing of pitches is paramount, that you can’t just throw twenty-four straight curveballs.

But Lance McCullers sure did throw twenty-four straight curveballs in the biggest moment of his career. And it worked.

McCullers isn’t the only one relying more heavily on his best “secondary” pitch. Patrick Corbin, who has dismantled the Giants twice this season, is largely ignoring the fastball and relying more on his slider and his sinker, while mixing in a curveball. The last two years he’s thrown his slider around 38-39% of the time compared to his career average of 28.2%, while his fastball rate is down to 18.3% from 30.3%.

And it’s working. He’s gone from league average starter to Cy Young candidate, and in large part it’s because he’s moving away from the four-seam and using his best pitch more often.

You’ve probably heard that Chris Stratton has an elite-level spin rate on his curve. Out of all pitchers who pitched more than 500 times, Stratton had the highest average spin rate. It’s his best pitch, theoretically.

In 2017, opponents hit .116 and slugged .163 against his curve with a 36.7% whiff rate. He also only threw it 18.5% of the time. Stratton’s distribution of pitches is pretty traditional. Four-seam over half the time, with his secondary pitches all around 10-15%. Stratton seems like he could benefit from the McCullers or Corbin strategies of just throwing his best secondary pitch more often.

But Stratton hasn’t thrown his curve more in 2018. In fact, he’s thrown it less, down to 15.8% of the time, and his fastball percentage has gone from 40% to 57%. What gives?

For one thing, Stratton’s curve simply hasn’t been as reliable for him this year, and he hasn’t needed it to be successful. Opponents are hitting .227 and slugging .364 against his curve in 2018 and he’s getting fewer whiffs on it, down to 25%. In his disastrous start against the Dodgers, he didn’t have command of his curve, and Chris Taylor put one over the centerfield wall. In his great start against the Diamondbacks on April 18^th, he only threw eleven curves. In his quality start against the Braves most recently, the fastball was key.

Perhaps Stratton is less confident in his curveball. He’s only thrown fourteen pairs of curveballs back-to-back and none of those sequences have come against right-handed hitters. Baseball Prospectus’ tunneling information suggests that he should be able to throw consecutive curveballs. Without getting too granular into numbers, Stratton has consistent release points with his curve, his curves separate in the air late, and they separate a good distance from each other.

Here’s a pair Stratton threw against Cody Bellinger:

Those yellow triangles in the middle of the flight path indicate the decision-making point for the hitter. At that point, the batter must decide if, when, and where to swing. The location on that second curveball was lousy, but Bellinger swung over the top of it and grounded out. Bellinger was probably expecting the ball to be higher in the zone because the pitch was roughly in the same spot as the decision-making point.

That second curve was also thrown about a mile and a half harder, and varying speeds is crucial in backing up pitches of the same type. Stratton doesn’t always succeed in varying the speed of his curve.

One of the reasons McCullers can throw his curve so much is that he excels at varying his speeds. He can go as low as 80 MPH to as high as 90 in a game. The slow(er) curve has about four more inches of vertical movement than the fast curve. It’s in effect, two different pitches.

The same with Corbin. His slider, though it doesn’t vary as much, can go between 78 and 83 and it behaves differently depending on velocity.

Stratton, though, doesn’t vary the speeds on his curve as widely. His curve generally goes between 74-79 MPH. The standard deviation on his curveball velocity this season has been 1.22 MPH. That second curve Stratton threw to Bellinger had a difference of two standard deviations away, which certainly helped him throw it back-to-back.

The Giants are smart, and if the solution were “vary the speed on the curveball and throw more of them,” I’m sure they would have tried it. Stratton shouldn’t go out and throw twenty-four curveballs in a row, but it seems like he could stand to throw it more than he has in the past.