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How is Nick Pivetta doing this?

It’s all about his two main pitches.

Los Angeles Angels v Boston Red Sox Photo by Kathryn Riley/Getty Images

The Red Sox have been one of the big surprises in baseball, still sitting in first place in the division more than a quarter of the way through the season. It hasn’t been smooth sailing all year, but they are winning games and showing a resilience they hadn’t shown at all last year, and rarely showed in 2019. And in looking around the roster, it’s hard to point at anything else besides their rotation as the biggest surprise among position groups. And if you want to narrow things down even further from there, you needn’t look further than Nick Pivetta, who has been far and away the biggest surprise on the Red Sox roster.

The righty was all but guaranteed a rotation spot to start this season by virtue of his lack of minor-league options, but the expectations were not very high. He appeared on the verge of losing his career with the Phillies before Boston traded for him late last summer, and his two good starts to close last season were hard to look at over the rest of his career. Many were expecting him to revert back to what he looked like with the Phillies, including yours truly. In fact, my expectation was that he’d be in the bullpen by Memorial Day. That is clearly not going to happen.

Instead, Pivetta has an argument as being the team’s best starter right now. I’m not sure I’d go that far, but I’m also not sure the distinction matter much. Pivetta has been good. Full stop. He’s made eight starts this season, totaling 42 23 innings, and he’s pitched to a 3.16 ERA with a 3.70 FIP. How is this happening?

There’s two main columns on Pivetta’s stat sheet that explain his season to this point in my mind: The home runs and the walks. The home runs are the biggest positive here, as he has allowed just three homers on the year for a rate of just 0.6 per nine innings. On the other hand, he’s also walking more batters than ever before, with his 13 percent rate coming in three percentage points higher than his previous career-high, a mark that came in his rookie year. So is this balance sustainable, or is this season so far simply a house of cards just waiting to come down?

I want to start with the homers part of this, because this is really the most important part of what Pivetta has done so far this year. Home runs and hard contact in general has been a major issue for Pivetta over his career, as he’s routinely allowed homers at a rate higher than the league-average, including about two per nine innings over the previous two seasons. Before the season in our season preview series, we pointed to avoiding barrels being the biggest key for the righty this year. He’s done that in a big way, with a barrel rate that puts him in the top quarter of the league after consistently being in the bottom quarter of the league in every other year of his career. (An explanation on what exactly a barrel is.) And he’s getting this done thanks to the way he is pitching and his top two offerings in particular.

Everything Pivetta does works off of his fastball, which has been the case for his entire career. The four-seam is his most-used pitch every year, though the rate at which he is throwing it is up a bit this year. His velocity is also ticking back up and sitting at 95 mph again after a brief drop off last summer. Things don’t look too different in terms of usage, spin, or velocity compared to years past, but the quality of contact against the pitch in terms of average exit velocity is the lowest it’s been since 2018, and the expected wOBA is the lowest it’s ever been by a wide margin. The reason comes down to location. Pivetta has done a better job of working up in the zone this season, something he didn’t do much back in 2019. It’s not perfect and there are still some balls being left over the plate, but it’s an improvement. Below you can see a heat map comparing the location of his fastball in the two seasons.

2019
2021

A fastball can only do so much, though, and Pivetta’s biggest problem for much of his career has been a lack of a secondary to really pair with the heat. His slider has typically been a mix-up pitch he threw sparingly, but this year he’s elevated the offering to the pitch he uses the most after the fastball. And it’s working wonders. The pitch is getting a ton of whiffs at 32 percent, and it’s resulting in a similar amount of hard contact and similar expected results as compared to the fastball. And it’s an example of the breaking ball working perfectly off the fastball. There’s about a 10 mph difference between the two pitches, and Pivetta has done a better job of burying the pitch down in the zone or below it to his glove side, changing the eye level of the batter. Again, you can see a comparison below between where he is throwing the slider now versus 2019.

2019
2021

It seems the way these two pitches are playing off each other is resulting in a lot fewer barrels, even if he’s left some of each over the heart of the plate this season. The flip side has been the extra usage of his slider has seemingly played a big role in his walk rate climbing. The trade-off has worked to this point, however, and Pivetta seems incredibly confident that it will continue to work. He’s working with a poise on the mound of a guy who trusts everything he throws and knows he’s going to have success. You can see it with his attitude, and really with the pace at which he is taking the ball and throwing it immediately all game long.

I’m still a bit skeptical of what Pivetta is doing right now and whether or not he’ll be able to keep it up. Even with his control improving a bit his last couple times out, it still feels like these walks will come to bite him a bit. We also know this is a league of adjustments, and batters will certainly adjust to the way Pivetta is pitching and take advantage of some of these mistakes if they continue to be thrown. At the same time, there’s a long way for the righty to drop before being unusable, or even below-average. At the very least, I’m off the train of expecting a move to the bullpen, and I’m moving closer and closer to outright confidence in him with each of these starts.

Pivetta takes the mound again Thursday night against the Blue Jays, and the ultimate test of his success will be whether or not he can overcome the OTM jinx.