Somewhat surprisingly, Matz's velocity hasn't changed, not really. Matz's sinking fastball averaged 94.6 mph last season, and it's at 94.4 mph this year. It was 94.2 mph when he threw 7.2 shutout innings against Atlanta on May 4, and it was 94.1 mph when he allowed six earned runs without a strikeout against Atlanta last week. So don't worry about the radar gun. Instead, pay attention to ...
Too much spin?
"There were balls definitely up," Matz told local media after last week's tough outing in Atlanta, but he didn't seem certain if the elbow had anything to do with it. What we do know is that he had his highest spin rate of the season on his sinking fastball, at 2,125 rpm. Over Matz's previous 10 starts, nine had been consistently between 2,004 rpm and 2,088 rpm; one, on May 20, had actually been at 1,966 rpm.
High spin is great on a fastball when you want to induce swinging strikes and popups, because it allows a ball to defy gravity for slightly longer and stay up. It's the opposite of great when you're throwing a ball that's supposed to sink, and Matz got less movement on the pitch than he had all season. If this sounds familiar, it should; Jeurys Familia got too much spin while trying to quick pitch his sinker during Game 1 of the World Series last year, and since it stayed up rather than dropping, Alex Gordon crushed it for a home run.
We can't say with certainty that Matz's elbow condition directly caused that, but we do know that there was a change in spin while he was dealing with a change in his health. That's not the only change …
"I definitely wasn't finishing my pitches last time in that fifth inning," Matz continued. He's not wrong. Statcast™ can measure extension, or the distance in front of the mound a pitcher releases the ball from. No one really throws from 60 feet, 6 inches, and most pitchers decrease that distance by five to seven feet based on their stride and height.
Usually, Matz's extension on his fastball is just over 6.5 feet. In 10 of his first 11 starts, his fastball extension was consistently between 6.5 and 6.6 feet, and it had gone up to 6.7 feet in his June 18th start. In Matz's most recent start, it was down to 6.3 feet.
We're still learning how much of a difference is required to be statistically significant, but it fits with the change in spin rate. Last time out, Matz didn't extend as much and saw his spin rate change, and we know he's trying to adjust to what's going on with his elbow. Pitchers adjust all the time, of course, it's just that changing to protect one area can often lead to injuries elsewhere.
No more sliders
When Matz debuted last year, his arsenal included a slider, one effective enough that catcher Travis d'Arnaud called it "devastating." Though it was never his best pitch or close to it, along with his curveball, the slider provided a different look that kept hitters from sitting on his fastball.
But in an effort to protect his arm, Matz is no longer using the slider, as he admitted earlier this week. In Matz's first nine starts (during which he had a 2.28 ERA and .272 on-base percentage against), he threw the slider just over 14 percent of the time. Over his past four (during which he has a 5.91 ERA and .358 OBP) against, that's dropped to only five percent, and even that's higher than you'd expect to see on Thursday -- he's thrown all of one slider in the past two games.
None of which is to say that Matz can't still be effective, of course. He held the Braves scoreless through four innings in that last start before running into trouble, and when CC Sabathia had surgery to remove a bone spur in 2012, it was revealed he'd likely been pitching with it since before he'd signed with New York in 2008 -- and Sabathia had given the Yankees 905 innings of 3.22 ERA ball to that point.
We just know what to look for, now. Matz has a sore elbow, and he already has an elbow surgery on his resume; to compensate, he's changed his pitch selection, and his spin and extension have changed, too. As Matz faces the Cubs on MLB Plus, now you know what to watch for.