Jose Berrios has a 6.75 ERA. His FIP is 5.63. He’s walked 16% of the batters he’s faced this season. He’s averaging more than 20 pitches per inning, and in two starts he has completed just 9.1 innings. He also has three good, major league-quality pitches with the potential for a fourth. He’s struck out more than 30% of the batters he’s faced. He could win Rookie of the Year, and — with arguments to come from Lucas Giolito, Tyler Glasnow, Alex Reyes, Blake Snell, and Julio Urias — he might be the most exciting pitcher to make his big-league debut this season.

Berrios doesn’t turn 22 until the end of the month, but he has ridden a quick and steady ascent to the majors. In 2014, he dominated High-A and held his own in a handful of starts at Double-A. Kiley McDaniel ranked him the 24th-best prospect in baseball during the 2014-15 preseason before he proceeded to mow down opponents in Double-A and Triple-A, striking out more than 25% of batters at both levels and walking less than 6% of them. Berrios entered Spring Training with an outside shot to win a starting job, but struggled with command in both his major-league and minor-league games.

In three minor-league starts this year, Berrios still produced his share of walks. But also struck out 20 of the 66 batters he faced and allowed just three runs, earning a promotion when Ervin Santana hit the disabled list. His first two starts have been a mixed bag, featuring both flashes of the potential that make him a top prospect with a comp to Pedro Martinez and show how he can be successful in the big leagues, but also an inability to consistently attack hitters in the strike zone, leading to unfavorable counts and walks.

The chart below shows league-average plate-discipline numbers as well as Berrios’ own numbers over his first two starts.

Jose Berrios Plate Discipline After Two Starts O-Swing% Z-Swing% Swing% O-Contact% Z-Contact% Contact% Zone% League Average 29.3 % 63.1 % 45.4 % 62.3 % 85.9 % 77.9 % 47.7 % Jose Berrios 28.3 % 54.2 % 39.7 % 60.0 % 84.4 % 74.7 % 43.9 %

Given the lack of innings, the numbers one finds here aren’t necessarily indicative of Berrios’ future performance. What they do illustrate, however, are the adjustments Berrios will need to make as he faces a better caliber of hitter. Consider his zone percentage, for example. Berrios is throwing just 44% of pitches in the zone. Not coincidentally, Berrios’ swing percentage is also below average. Last season, there were nine qualified pitchers who threw fewer than 44% of their pitches in the zone, and all of them had an O-Swing rate of at least 30% on the season. Not a single qualified pitcher recorded a total swing percentage under 41%, and the leaders (bottom dwellers) of that category — which included Yovani Gallardo, Chris Heston, and Ubaldo Jimenez — suggest that this isn’t necessarily company Berrios should be aiming to keep. He can throw pitches out of the zone, but hitters need to swing at those pitches in order for him to be successful.

It’s probably natural that batters, facing a new pitcher, would exhibit some tentativeness, but Berrios has had trouble commanding pitches other than his four-seam fastball. His four-seam fastball has had a good amount of success, responsible for a healthy 16% whiff rate, and with his curve has been responsible for 11 of his 13 strikeouts, per Brooks Baseball. The chart below from Baseball Savant features a heat map for Berrios’ fastball, showing a pocket at the top of the strike zone, as well as a convergence on the outside edge of Berrios’ arm side as well.

For Berrios to be successful, he must walk fewer batters and be more efficient with his pitches. Eleven of 43 batters have gone to three-ball counts and just two of his total plate appearances have ended on the first pitch. Berrios has recorded a first strike against 23 of 43 batters, but when he throws something other than his four-seam fastball, he’s gotten strike-one just 11 of 27 times. This pattern continues on 1-0 counts: just seven of 15 non-four-seamers were able to even up the count. When he’s gone to a three-ball count, he’s primarily trusted his fastball, throwing his four-seamer 15 of 18 times, ending up with six walks on the four-seamer as well as one on the curve.

That curve has been very effective in the early going, particularly fooling right-handers like Jose Altuve. For example: on a 1-2 count to Altuve during his most recent start, Berrios threw this curve:

As you can see, Altuve bails, under the impression that the pitch is coming right at him. However, the screenshot below depicts the moment the ball lands in JR Murphy’s glove.

As FOXTRAX shows, the pitch was a strike. Certainly Murphy felt it was a strike. The pitch was called a ball, however. Murphy disagreed. He got into an argument with umpire Jerry Layne and was ejected.

As Kurt Suzuki put on his catcher’s gear, Berrios took a few warm-up tosses. Then when Suzuki was ready, he took a few more. After a delay of nearly five minutes, Berrios threw the same pitch again.

Strike three.

The curve isn’t a traditional 12-6 pitch, moving back towards the strike zone from the right-handed batter’s box. Once again, Altuve moves his back foot away from the plate. The umpire recognizes the pitch this time, and Berrios records a strike-three looking.

The four-seamer has worked and the curve has been competent thus far. Berrios’ best pitch by the scouting reports, however, is the changeup. That pitch hasn’t been as effective, though. Berrios’ change, a pitch that moves down and away from lefties, is a chase pitch. It can work very well when ahead in the count, but with Berrios often pitching from behind, it loses its strength. He has thrown the pitch just 26 times in two games. It’s been taken for a strike five times, inducing only seven swings and eliciting just two swings and misses. He’s used the pitch ahead in the count just five times, and just eight times with two strikes. Using the zone map from Brooks Baseball to show every change, here is where those pitches have gone so far.

If he isn’t pitching ahead in the count, and he’s not throwing strikes, it is going to be tough for Berrios to get swings on pitches located out of the zone. As for the one changeup that landed in the middle of the zone? Not a good result:

Berrios can pitch the ball where he wants generally. He earned a 65 grade on his control from Baseball America, and a 55/60/60 in command from Dan Farnsworth, who picked Berrios as his Rookie of the Year. That Berrios has had some success in his first two starts without positive results from his best pitch should be taken as a good sign. Presumably, he will be able to locate the pitch a bit better in the future and use it counts that are more advantageous.

Berrios’ fourth offering is a sinker that tails away from lefties and in towards righties. The two-seamer can be an effective pitch, as seen here, moving away from left-handed batters like Preston Tucker.

Compare that to the four-seam fastball from an equivalent angle. Berrios has better command of it, and it stays in the zone and up over the plate.

It’s not difficult to see why Berrios goes to the four-seamer when he needs a strike; however, if hitters are ready for the pitch and know it’s coming, they will eventually be able to square up against it. Two-seamers down in the zone are often used to induce weak contact and get quick outs, something from which Berrios could benefit. Right now, Berrios is making every pitch a strikeout pitch, and it’s a good thing to have that ability. Unfortunately, throwing most of your pitches out of the zone for whiffs can lead to long at-bats during which the batter can gain an advantage. Berrios has either not yet been able to command the sinker, or is intentionally pitching it out of the zone as this heat map from Baseball Savant reveals:

The sinker is probably Berrios’ fourth-best pitch and might always be, but it could also be key in making the rest of his pitches work. If Berrios can get the same movement lower in the zone, he can get called strikes and ground balls on the pitch, enabling him to record shorter at-bats and shorter innings while allowing greater use of his put-away pitches in favorable counts. Berrios has not gotten the overall results he has desired, but he has really good stuff that shows a lot of promise. Everything might not come together all at once, but there is a lot to like in what he’s show thus far.