This time last year, Jeff Sullivan posited that the Indians might have assembled the best pitching staff in baseball history, a distinction that unsurprisingly included one of the best collections of starting pitchers ever. Even though the club wasn’t able to translate their success into October glory, it would be hard to pin whatever shortcomings the team exhibited on the rotation, the worst regular member of which, Josh Tomlin, recorded “only” a league-average FIP. It was an impressive season.

Perhaps surprisingly, the 2018 campaign has seen the Indians repeat that success. The rotation as a whole leads baseball with 19.9 WAR, with its four best starters — Trevor Bauer (6.0 WAR, fourth in baseball), Corey Kluber (4.9 WAR, ninth), Carlos Carrasco (4.1 WAR, 11th), and Mike Clevinger (3.9 WAR, 12th) — ranked among the top 12 of the league by that metric. That quartet has already exceeded their combined WAR from 2017 by half a win with a month to go. Notably, that isn’t even the only way in which the rotation has improved.

Instead of Tomlin, the Indians have turned to rookie starter Shane Bieber since the end of May. In 15 starts, Bieber’s has produced a 4.66 ERA but has also posted an incredible 3.23 FIP and 2.0 WAR in a mere 85 innings. He strikes out over a batter an inning (9.21 K/9) and has excellent control of his pitches, as evidenced by a top-10 walk rate (4.2%). Putting those figures two together, Bieber’s 5.8 K/BB is exceeded by only six pitchers with at least 80 innings pitched. Some impressive names are counted among those six, including Clayton Kershaw, Chris Sale, Justin Verlander, and Bieber’s teammate, Kluber.

The Indians seem to have struck gold with Bieber. While the team doesn’t seem to need it this year — thanks to the remarkably weak AL Central — Bieber is a key piece for the Indians in the future. His repertoire, ability to deploy his pitches, and command make him an especially valuable (and foundational) starter.

This jump forward for Bieber was a bit still unexpected. Sure, he threw a seven-inning no-hitter in his last minor-league start, and his outstanding command led to just 19 walks in 277 career minor-league innings. Other than that, Kiley McDaniel and Eric Longenhagen felt his raw stuff seemed fairly pedestrian. They graded his pitches as follows: 50 fastball, 60 curve, 50 slider, 50 changeup. The last line of from their Cleveland list is key here for Bieber’s development into a potential rotation weapon.

The stuff, alone, projects to the back of a rotation, but Bieber’s ability to locate gives him a chance to be a mid-rotation arm. It’s possible he has elite command and becomes something more.

The command of Bieber’s pitches allows his stuff to play up, similar to many other pitchers who have garnered success in the majors. Obviously things have gone fairly well for Bieber, and he advanced to the 64th-best prospect in our midseason update. In addition to his incredible command, it’s worth considering the individual pitches on their own merits, apart from that command.

Bieber’s fastball — thrown nearly 57% of the time — doesn’t light up radar guns, averaging 93.2 mph. (That’s precisely average for MLB starters this season.) What the pitch lacks in velocity, it makes up for in movement. The fastball has 6.2 inches of arm-side run (decidedly top-tier among starters) and 9.1 inches of rise (slightly above league-average). This movement and lack of velocity makes Bieber’s fastball a pitch that doesn’t generate many whiffs (only 15.2% of swings); however, it does generate many grounders, at 43.1% per ball in play. Because of this grounder generation, Bieber’s batting average against on fastballs is fairly high at .319. In this he is a little unlucky, as Statcast thinks it should be something closer to .279.

The second-most common pitch in Bieber’s arsenal is his slider, thrown 22.6% of the time. The pitch mostly works on the 12-6 plane, with 1.4 inches of glove-side movement and 0.7 inches of drop. This pitch is where Bieber gets his whiffs, with 41.4% per swing. When put in play, the pitch gets put on the ground 43.1% of the time with a batting average against of .239. The pitch is worth 1.25 runs per 100 pitches, good for 38th in baseball among pitchers who have thrown 80 innings.

Close behind the slider is Bieber’s curveball, thrown 16% of the time. The curveball and slider have an interesting interplay, as there is only 3.4 mph difference between the latter (83.6 mph) and former (80.2). Moreover, the curveball also works on the 12-6 plane with a more distinct arc than the slider, dropping 7.6 inches with 4.0 inches of glove-side action. You can see this similarity in the two pitches (curveball on the left, slider on the right) from his August 26th start against the Royals.

The raw stuff seems to be the better on the curveball, but it has been knocked around more than the slider; a batting average against of .308 and an ISO against of .212. Again, Statcast suggests that these numbers shouldn’t be this high given the exit velocities and launch angles, giving hope that the pitch has more than what it has shown this season.

Finally, Bieber occasionally slips in a changeup — just under 5% of the time. While it seems like a pitch that could play well against his fastball — similar horizontal movement out of the same slot — it has one major problem: the separation with the fastball in terms of velocity and vertical movement is too little. While the fastball comes in around 93.1 mph, the changeup only is 5 mph slower at 88.1. As a result, the difference in the vertical movement is only two inches. That lack of separation has gotten the pitch pounded to tune of a .300 batting average and .400 ISO in a very small sample. This problem of his changeup being too firm goes back to his college days, and it does limit him as a pitcher. If he were to soften the pitch a few mph and retain the horizontal movement, it could be a complementary piece to the rest of his arsenal against left-handed hitters.

Again, all these pitches play up thanks in part to Bieber’s command of them. He locates the pitches well, entices hitters to swing at his breaking offerings, and has the ability to keep the ball on the ground. Despite this — or possibly because of the ground-ball rate — he has allowed a much higher BABIP than what might be expected of him. It seems like he is only a couple tweaks away from being an even better starter than what he already is given what his stuff suggests.

Shane Bieber rounds out Cleveland’s rotation in an impressive fashion. While he likely will not get many starts in the postseason, he is a well above-average fifth starter, and he will continue to help push them to October. More importantly, given his age and future potential, he is a building block for the team going forward as Corey Kluber and Carlos Carrasco continue to age. He leaves them in a position to not only compete now, but continue to compete going forward.