Meet the Class of 2019: The MLB players who graduated to stardom

Young players are dominating baseball like never before, but it takes more than some success on the field to become a star. With that in mind, we asked our Jeff Passan and David Schoenfield to make and grade the cases for 20 2019 breakout players to ultimately decide who graduated to stardom this season.

While the 2019 class climbs the stairs in alphabetical order, wearing their (baseball) caps and gowns, it will be up to Professor Passan and Dean Schoenfield to determine who has earned their degree in superstardom. Will a Class of 2019 diploma be waiting for your favorite player?

Pete Alonso, New York Mets

Who he was in March: The power-hitting first baseman led the minors with 36 home runs in a 2018 season split between Double-A and Triple-A, but the Mets also had Dominic Smith and a glut of veteran infielders who also could play first base if needed (Todd Frazier, Robinson Cano, Jed Lowrie). Alonso had to win the job in spring training.

His 2019 case for stardom: Home runs. Lots of them. He destroyed Cody Bellinger's National League rookie record, reached Mark McGwire's 1987 rookie total of 49 and is chasing down Aaron Judge's rookie record of 52 as he battles for the overall MLB lead.

Professor Passan proclaims: There is a very simple equation. Home runs + New York = Stardom. Pete Alonso hits lots of home runs. Pete Alonso plays in New York. Pete Alonso is a star.

Yordan Alvarez, Houston Astros

Who he was in March: A promising slugger who hit .293 with 20 home runs in 88 games across Double-A and Triple-A in 2018, but with questions about his defense and no immediate path to playing time with the Astros.

His 2019 case for stardom: Well, the American League has the DH rule. Alvarez tore apart Triple-A Round Rock and received a promotion to the majors on June 9. He homered in four of his first five games and has terrorized major league pitchers ever since with one of the highest OPS totals since his recall.

Professor Passan proclaims: Since his June 9 debut, Alvarez has been the best hitter in the American League. Better than Mike Trout. Better than his teammates Alex Bregman and Jose Altuve. The. Best. That's a star.

Tim Anderson, Chicago White Sox

Who he was in March: A toolsy and athletic shortstop with some pop (20 home runs in 2018) and speed (26 steals), but with a .258 career average and .286 OPB through three seasons.

His 2019 case for stardom: He still swings at everything but has a chance to win the AL batting title. If he does, his .258 average would be the lowest a batting champ had entering the season.

Professor Passan proclaims: A batting title is wonderful. A dozen walks in almost 500 plate appearances is frightening. A .399 BABIP is unsustainable. Two outta three, in this case, is bad. But this is Tim Anderson. The bat-flippingest make-baseball-fun ambassador there is. The well-rounded skill set makes it a yes.

Josh Bell, Pittsburgh Pirates

Who he was in March: A heralded prospect coming up through the Pirates system, Bell slugged 26 home runs as a rookie in 2017 but just 12 in 2018. He had a decent .357 OBP, but the lack of power was concerning.

His 2019 case for stardom: Bell spent the offseason working with a private hitting instructor named Joe DeMarco, and the pair overhauled Bell's body position, mechanics and approach. He hit six home runs in April and then .390 with 12 home runs in May, and the big first half earned him an All-Star nod. He has slowed down since but is still at 37 home runs, 116 RBIs and an OPS well north of .900.

Professor Passan proclaims: This is a tough one. Bell was perfectly good his first two full major league seasons. Then he turned into a monster in the first half this year. Since the All-Star break, he has been almost a carbon copy of his first-two-years self, which is decidedly not a star. Wait. Earnest Bell wants a word? Uh. Never mind. He's a star.

Walker Buehler, Los Angeles Dodgers

Who he was in March: The former first-round pick out of Vanderbilt had fully recovered from Tommy John surgery and finished third in the Rookie of the Year balloting in the National League after going 8-5 with a 2.62 ERA. His dominant performance against the Rockies in the NL West tiebreaker game -- one hit in 6 scoreless innings -- culminated a run in which he posted a 1.55 ERA over his final 12 starts. With a fastball that averaged 96.7 mph, a full complement of off-speed pitches and excellent control, he looked like a potential Cy Young contender.

His 2019 case for stardom: He's 13-3 with a 3.15 ERA and 202 strikeouts in 171 innings while issuing just 30 walks. When he's on, he's really on: He has allowed no runs in eight starts and one run in five starts and had games with 16 and 15 punchouts.

Professor Passan proclaims: Last year, after beating the Rockies in Game 163, Buehler was asked if he knew he was going to win. "I won't say 'yes,'" he said, "but yes." It's not just the fastball and strikeouts. Buehler walks and talks like a star too.

Luis Castillo, Cincinnati Reds

Who he was in March: One of the hardest-throwing starting pitchers in the majors, Castillo had a 4.30 ERA in 2018 in his first full season. Was he a one-trick pony or could he back up his high-octane heater with a more refined approach to pitching?

His 2019 case for stardom: Castillo stormed out of the gate with a 1.76 ERA through his first nine starts. He earned his first All-Star selection and is 15-6 with a 3.22 ERA, improving his strikeout rate from 23.3% to 28.9% while also cutting down on his home runs.

Professor Passan proclaims: Castillo since July 1, 2018: 260 innings, 291 strikeouts, 30 home runs allowed, 3.04 ERA -- while pitching in the Great American Band Box. His fastball-changeup combo is a Tyson-prime right hook/right uppercut. Do it for one year? OK. For two? Star.

Mike Clevinger, Cleveland Indians

Who he was in March: That other guy in the Cleveland rotation, the one with the long hair that made him look like he belonged at a skateboard park instead of on a major league mound. He had an under-the-radar breakout season in 2018, going 13-8 with a 3.02 ERA, but that made him just the third-best starter on the team behind Trevor Bauer and Corey Kluber.

His 2019 case for stardom: He missed time early in the season with a back injury and then 10 more days with a sprained ankle, but when he has pitched he has raised his game to another level, going 11-3 with a 2.68 ERA and 149 K's in 107 innings.

Professor Passan proclaims: Psssssst. He was a star last year too. It just takes an extra year for anyone to recognize it when you play in Cleveland.

Rafael Devers, Boston Red Sox

Who he was in March: A talented but unproven young hitter. He won a ring with the Red Sox in 2018, but his first full season was a bit of disappointment as he hit just .240/.298/.433. Still, he was just 21, so there was hope for growth.

His 2019 case for stardom: He grew. Devers began the season without a home run in his first 32 games, but then everything suddenly came together and he's hitting over .300 with 50 doubles and 30 home runs. He and teammate Xander Bogaerts became just the 13th and 14th players to reach both figures in one season since 2000.

Professor Passan proclaims: Came up at 20 with a stratospheric start. Returned to earth, struggled and slumped his second season. Put everything together this year and now leads the AL in total bases. That's actually a pretty archetypal star turn -- from wunderkind to learning to fully realized.

Jack Flaherty, St. Louis Cardinals

Who he was in March: Part of the star-studded 2018 rookie class, Flaherty went 8-9 with a 3.34 ERA at age 22, finishing fifth in the Rookie of the Year vote. With his perfect pitcher's build (6-foot-4, 205 pounds) and elite stuff, there were high expectations for his sophomore season.

His 2019 case for stardom: It was a slow start, but he has arguably been the best starter in the majors in the second half with a 1.05 ERA in 12 starts and an opponents batting line of .157/.226/.240. Overall, he's 10-8 with a 3.05 ERA and 206 whiffs in 174 innings.

Professor Passan proclaims: He was sneaky excellent last year. All of this -- especially the brilliant second half -- makes this a no-brainer star turn.

Lucas Giolito, Chicago White Sox

Who he was in March: Once regarded as maybe the top pitching prospect in the game, his first full season in the majors was a disaster with a 6.13 ERA. At least he started 32 times, about the only positive from his 2018 season. His future was cloudy.

His 2019 case for stardom: Maybe the most improved player in the league, Giolito made the All-Star team and finished 14-9 with a 3.41 ERA and in about the same number of innings fanned 103 more batters than in 2018.

Professor Passan proclaims: He has turned in a wonderful 2019. He has a chance to be a workhorse in an era when workhorses simply don't exist. But he's not a star yet. This is nothing against Giolito. It is a bias against pitchers succeeding at the major league level for one season -- especially after one as bad as 2018. He made adjustments this year; the question is whether the adjustments of hitters next year will change the outcome. If not, he'll headline this list.

Ketel Marte, Arizona Diamondbacks

Who he was in March: He was a nice player, coming off a nice 2018 season in which he hit .260/.332/.437, and after hitting just eight home runs his first three seasons in the majors, he showed a little pop with 14 home runs and 12 triples. He had moved off shortstop to second base, however, and the Diamondbacks were also going to try him in center field.

His 2019 case for stardom: Wow. The skinny slap-hitting shortstop prospect for the Mariners developed into a rocket-hitting masher, hitting .329 with 32 home runs, all while playing a surprisingly good center field (and filling in at second base as well).

Professor Passan proclaims: An OPS near 1.000 for a 25-year-old who had a huge tool set and finally translated it warrants a yes. Star.*

* pending ball that doesn't fly like it's rocket-fueled.

Jeff McNeil, Mets

Who he was in March: He surprised by hitting .329 in 63 games as a 26-year-old rookie, but the Mets had so much confidence in him that they traded for Robinson Cano and signed Jed Lowrie. Maybe they would try him in the outfield and turn him into a utility guy.

His 2019 case for stardom: If you can hit, the team will find a place for you in the lineup. McNeil has hit .318, but the big surprise has been the 23 home runs on his way to a 5-WAR season. He has started at least 14 games in left field, right field, second base and third base.

Professor Passan proclaims: Buying the bat all day, every day. Seriously, have you ever seen McNeil's actual bat? It looks like a club. It has no knob and a ridiculously thick handle. It's practically a medieval weapon. In other words, McNeil would have been a star in the Byzantine army too.

Chris Paddack, San Diego Padres

Who he was in March: Stolen from the Marlins for Fernando Rodney in 2016, Paddack returned from Tommy John surgery to make 17 starts in the minors in 2018 with a 2.10 ERA -- and just eight walks in 90 innings. The Padres gave him a shot at making the rotation.

His 2019 case for stardom: He did, start off with a sizzling April and finishing 9-7 with a 3.33 ERA over 26 starts, including an impressive 150 strikeouts to just 31 walks.

Professor Passan proclaims: The Giolito Corollary. One major league season of excellent pitching does not a star make. Next year's list could have a pretty sweet rotation, though.

Marcus Semien, Oakland Athletics

Who he was in March: That guy who made all those errors that one season? He was a nice player and his fielding had improved, but he had never posted an OPS+ above league average.

His 2019 case for stardom: He's hit more than 30 home runs, he's played good D and he's played every game for the A's. His 7.4 Baseball Reference WAR is the second highest for a shortstop this decade (Francisco Lindor had 7.9 in 2018).

Professor Passan proclaims: Regardless of what he does with his bat, Semien is star-adjacent on account of his glove alone. So grain-of-salt this as you may: It would be nice to see him do what he's doing again. Career .403 sluggers tend not to raise the mark by more than 100 points in a season. He has gotten better, but -- and this goes for Marte, McNeil and others -- how much of that is improvement and how much of that is the ball?

Mike Soroka, Atlanta Braves

Who he was in March: Part of the Braves' plethora of young pitching prospects, Soroka made five starts for the Braves in 2018 as a 20-year-old but missed the final three months with a shoulder strain and inflammation.

His 2019 case for stardom: He's not just a Rookie of the Year candidate but a Cy Young candidate, with a 2.60 ERA and the poise and feel for pitching of a 22-year vet, not a 22-year-old kid from Calgary.

Professor Passan proclaims: Ibid. Giolito/Paddack.

Eugenio Suarez, Cincinnati Reds

Who he was in March: He had slugged 60 home runs over the past two seasons and received an All-Star berth in 2018, but as a third baseman on a bad team in a league that featured Nolan Arenado, Kris Bryant, Anthony Rendon and Justin Turner at the position, he was still relatively anonymous.

His 2019 case for stardom: Now he's battling Pete Alonso for the MLB lead in home runs, and his unbelievable second half gives him a shot at breaking George Foster's franchise record of 52 home runs.

Professor Passan proclaims: In 2014, the Detroit Tigers needed a starting pitcher. They dealt for veteran Alfredo Simon, who threw 187 innings of 5.05 ERA ball worth minus-0.5 WAR. The return? A rookie named Eugenio Suarez, who, five years later, is most certainly a star, having hit like one for two years running.

Fernando Tatis Jr., San Diego Padres

Who he was in March: The consensus No. 2 prospect in the game behind Vladimir Guerrero Jr. -- though No. 1 onKeith Law's preseason list -- he hadn't played above Double-A and was just 20 years old, but the Padres gave him a chance to win the shortstop job in spring training.

His 2019 case for stardom: He broke camp with the Padres -- screw service time -- and soared past Vlad with a .317/.379/.590 line and some spectacular plays in the field before a stress reaction in his back ended his season in August.

Professor Passan proclaims: Everything about him, from the bat to the glove to the arm to the slide to the look, screams star. If we were ranking this list instead of going alphabetically, he'd be No. 1.

Gleyber Torres, New York Yankees

Who he was in March: He made the All-Star team and finished third in the American League Rookie of the Year voting in 2018 after hitting .271 with 24 home runs.

His 2019 case for stardom: Still just 22, he's about to become the first Yankees middle infielder to hit 40 home runs (Alfonso Soriano hit 39 in 2002). He's done that while playing a solid shortstop when Didi Gregorius was injured and then moving back to second base.

Professor Passan proclaims: He's the future Yankees shortstop and on the cusp of 40 home runs in his age-22 season a year after a Rookie of the Year-quality season. Yes. That is a star.

Kirby Yates, San Diego Padres

Who he was in March: A 32-year-old journeyman reliever who had been let go at various points in his career by the Red Sox, Rays, Indians, Yankees and Angels. The Padres claimed him off waivers in 2017 and he had a 2.14 ERA with 12 saves in 2018. Not that anybody outside of San Diego had noticed.

His 2019 case for stardom: In a year when it feels like every closer has struggled, Yates has been the one constant with a 1.21 ERA and an MLB-leading 41 saves.

Professor Passan proclaims: Just because he's 32 and well-traveled doesn't preclude Yates from being recognized for what he has become: the best reliever of 2019 and a star.

And there you have it, the members of the Class of 2019 are ...Pete Alonso, Yordan Alvarez, Tim Anderson, Josh Bell (thanks to Mr. Bell), Walker Buehler, Luis Castillo,Mike Clevinger, Rafael Devers, Jack Flaherty,Ketel Marte, Jeff McNeil,Eugenio Suarez,Fernando Tatis Jr.,Gleyber Torres,Kirby Yates. Better luck next year to all who just missed graduating this time.