7 player breakouts to believe in this year

May 26th, 2021

Every year brings big breakouts from the next wave of MLB stars. The 2021 season is no different.

But which new stars from the first two months will keep up their success? Here are the ones who look like they're for real. MLB.com's experts picked the breakout players whose early-season performance is worth believing in.

Here are seven 2021 breakouts we're buying. (All stats entering Tuesday's games.)

Vladimir Guerrero Jr., Blue Jays
Key stat: +29 swing/take runs (6 more than anyone else in MLB)

In the offseason, when we picked potential breakout players for 2021, I took Guerrero in the AL, noting his penchant for hard contact. The key for him, as was widely discussed entering the year? Lift the ball more, to better utilize that power. And so far in 2021? He’s done that, with a lower ground-ball rate, higher average launch angle and higher sweet-spot rate. He’s crushing the ball, with a 16.1% barrel rate that’s almost twice his career best prior to '21. In other words -- he’s doing it, what we all hoped would happen, crushing the ball and putting it in the air more.

But the thing that’s really put his game on another level this year? Increased plate discipline. He’s swinging less and making those swings count more. Guerrero has 29 swing/take runs, numbers which assign run values to each pitch based on outcomes and can quantify a player’s value in different parts of the zone. The notable result there? He’s chasing less. And he's made the most of the in-zone pitches he’s seen -- his 21 swing/take runs in the "heart" of the zone are the most in baseball. That indicates great plate discipline choices on those. He’s put it all together so far in 2021.
-- Sarah Langs

Carlos Rodón, LHP, White Sox
Key stat: 35.2% swing-and-miss rate

It took years of ups and downs, injuries and a brief foray into free agency last offseason, but Rodón is finally delivering on the promise that made him the No. 3 overall pick in the 2014 Draft. And this version of Rodón? Worth the wait. Among pitchers with 40-plus innings, the lefty ranks among MLB’s top five in ERA (1.27), Statcast’s expected ERA (2.12), strikeout rate (37.3%) and opponent batting average (.148).

Simply put, Rodón is dominating, and it’s not just the no-hitter, either. After a hiccup on May 15 against the Royals, Rodón was right back at it in his last start, blitzing through the Yankees’ lineup in the Bronx for 13 strikeouts and no walks in six scoreless innings. Many pitchers have one bat-missing pitch, but the new-and-improved Rodón has three yielding a whiff rate over 30%: a four-seamer with career-best velocity (95.1 mph), a slider that’s held opponents to 1-for-46 and a changeup to keep righties honest. With those weapons, this doesn’t look like a fluky hot streak. It looks like the start of a thrilling second act.
-- Andrew Simon

Jazz Chisholm Jr., Marlins
Key stat: 2 HR off 100+ mph fastballs

Chisholm batted .161 in his first big league callup last year. He's spent all of 2021 making us forget that. Jazz looked electric in Spring Training. He looked electric to start the season. And he continues to look electric now. The power-speed combo is what jumps out (five home runs, eight stolen bases, 88th-percentile barrel rate and 95th-percentile sprint speed in MLB) … but there's more.

Maybe the most intriguing thing about Chisholm is that he's already homered off two 100+ mph fastballs this season -- one off Jacob deGrom, one off José Alvarado -- making him the only player since pitch-tracking began in 2008 to hit multiple homers off triple-digit heat. Both of those fastballs were up and out of the zone, too. You don't just run into homers against those pitches. You have to be a skilled hitter. Chisholm's bat-to-ball talent must be real.
-- David Adler

Carson Kelly, D-backs
Key stat: .458 xwOBA

OK, yes, Kelly dealt with a broken toe and has only played 28 games in 2021. But among players with at least 100 plate appearances, he ranks in the top 10 in batting average (.338), slugging percentage (.613), and OPS (1.103), and his MLB-leading on-base percentage (.491) is 25 points higher than Mike Trout’s. For context, in 213 career games from 2016-20, Kelly slashed .221/.305/.396. In his first two seasons with the D-backs, his hitting was nothing to write home about, but now, in his third, his expected stats look just like Buster Posey’s. So … what happened there?

The change in Kelly’s game has been pretty simple: He’s being more selective. His overall swing rate is down 8.1 percentage points from 2020, and he’s chasing 5.5 percentage points less. He’s walked in 20.9% of his plate appearances compared to 4.7% last year. Kelly still doesn’t hit the ball as hard as some of the elite hitters he’s stacking up against (his average exit velocity is 88.5 mph, about in line with the rest of the league), but he’s making up for that by swinging at his pitch more often. That’s led to a huge spike in his barrel rate, from 4.3% in 2020 to 13.4% this season. And because Kelly is swinging at pitches he can barrel up, his batted-ball data actually backs up his sky-high numbers -- particularly his MLB-leading .463 weighted on-base average, which almost perfectly matches a .458 expected wOBA that ranks at the top of the league.

Luck has certainly been a factor in Kelly’s red-hot start. But the discipline is all him, and that’s as real a change as any.
-- Shanthi Sepe-Chepuru

Trevor Rogers, Marlins
Key stat: 64 K on 4-seamers + changeups (leads MLB)

There were several reasons to take Rogers more seriously in 2021 than last year’s 6.11 ERA suggested. The biggest one? He misses bats. Rogers has elite fastball velocity for a lefty starter at 95 mph, and he locates it high and to the arm side, pushing him to an MLB-most 46 strikeouts via the four-seamer. It’s a great sign moving forward that Rogers can butter his bread with the heater, but his changeup -- with superb dropping movement off the table -- gives him a promising "1B" weapon, too.

Rogers has mostly dominated by changing speeds with those two offerings, but even his slider is missing swings about 40% of the time. And check this out: Among those select starting pitchers with a 30%-plus strikeout rate since the start of 2020 (min. 250 batters faced), the man who’s also allowed the lowest barrel rate out of all of them is … you guessed it, Rogers. This guy misses barrels whenever he’s not missing bats altogether, and Miami has yet another young rotation stud to build around.
-- Matt Kelly

Cedric Mullins, Orioles
Key stat: .356 xBA vs. sliders

Mullins has always been a great defender in center field, but his bat lagged behind until this point in his young career. So far in 2021, that has changed dramatically. Entering play Tuesday, he was hitting .294/.366/.472 with six homers and six steals. There’s plenty of reason to think what he’s doing is sustainable because of the changes he made at the plate over the offseason.

First, Mullins decided to give up batting from the right side, and now hits exclusively left-handed. He was slashing just .147/.250/.189 as a Major Leaguer hitting righty. So far, it’s working out well -- entering Tuesday, he had an .849 OPS hitting lefty vs. lefty pitching.

Second, Mullins has become much more patient at the plate. His chase rate has decreased significantly -- last year, he swung at 32.6% of pitches out of the strike zone, and that figure is down to 26.6% this season. He’s also swinging at the first pitch less -- he swung at 34% of first pitches last season, and so far this season, his first-pitch swing rate is 24.3%. As a result, his whiff rate is down from 21.6% in 2020 to 18.6% in '21.

Mullins gets overlooked sometimes because he’s an Oriole, but keep an eye on him -- this might be a breakout season that signals more success to come for the 26-year-old.
-- Manny Randhawa

Freddy Peralta, Brewers
Key stat: .143 xBA against

It’s easy to be overlooked in a rotation that includes Corbin Burnes and Brandon Woodruff, but Peralta leads the Brewers in strikeouts (76) and has the lowest hits-per-nine-innings mark (4.3) among qualified pitchers. Not bad for a guy who wasn’t even guaranteed to be part of Milwaukee’s starting staff until a week before Opening Day. Peralta is not only missing a ton of bats (96th percentile whiff rate), he’s also inducing a lot of low-quality contact in the air this season. Of the 96 batted balls he’s allowed in 2021, 39 of them (40.6%) have been weakly hit fly balls, one of the highest rates in the game. Opponents are 1-for-39 (.026) on such balls.

In the past, Peralta threw a curveball for his primary breaking pitch. It was effective, but he didn’t go to it all that often (19.9%). This season, he’s replaced his curve with a slider in which he clearly has more trust, using it 32.7% of the time and throwing it in all counts. It’s allowed him to dial back his reliance on the four-seamer, which he used more than 75% of the time from 2018-20. The new combination is clearly working for Peralta, who has allowed a combined .140 average with 72 K’s in 157 at-bats ending on a four-seamer or slider. The 24-year-old’s emergence gives the Brewers’ rotation a “Big 3” that could be formidable for years to come, with Burnes, Woodruff and Peralta all under club control through 2024 or longer.
-- Thomas Harrigan