Heralded youngsters such as Ronald Acuña Jr. and Fernando Tatís Jr. have delivered on their promise with ease, but other top prospects can still take time to put it all together (look at Yoán Moncada last season). Other stars, such as Jeff McNeil, were never ranked on preseason prospect lists, and even veterans such as Max Muncy and Eugenio Suárez can explode after years in the bigs.

That makes identifying the next great hitter an inexact science, but that doesn’t mean it’s not fun to try. Similar to its picks for dark horse Cy Young Award candidates, MLB.com enlisted five reporters to identify breakout hitters for 2020, with each selecting one hitter per league. “Breakout hitter” could have a range of definitions of course, and some names here are certainly more recognizable than others. But for the purposes of this exercise, the writers were asked to select hitters entering their age-27 or younger seasons, with at least 300 Major League plate appearances, and who have yet to make an All-Star team or record a league-adjusted OPS+ of 120 or higher in a single season. Only offensive performance was considered; defensive ability is for another conversation.

With those parameters in mind, here are the picks:

AMERICAN LEAGUE

Eloy Jiménez -- OF, White Sox
Key number: 47.9% hard-hit rate

One could quibble with Jiménez’s placement here, given that he already slugged .513 with 31 home runs in 122 games last year, finishing fourth in the AL Rookie of the Year race. But his 117 OPS+ was just under our qualifying threshold, and it sure feels like the 23-year-old can do a lot more than he showed in 2019. A top-five prospect lauded for his hit tool and power, Jiménez improved in the second half (.870 OPS) and absolutely raked in September (.340/.383/.710 with nine homers), hinting at a high ceiling that he is fully embracing this spring.

Few hitters made hard contact on more of their batted balls than Jiménez, especially in the second half (51.1%). And over the final month, nobody hit more barrels -- batted balls with an optimal combination of exit velocity and launch angle. Take that demonstrated ability to crush baseballs and add a year of experience at handling Major League pitching -- which could help improve a 134-to-30 strikeout-to-walk ratio -- and you have a young hitter who may be ready to emerge as a star at the plate.
-- Andrew Simon

Vladimir Guerrero Jr. -- 3B, Blue Jays
Key number: 118.9-mph exit velocity

We’re all waiting for this, right? Guerrero obviously didn’t come close to his expectations, and Acuña, Tatís and Jiménez all made the big league transition look much easier. But none of them can knock the baseball as hard as “Vladito.” Not only was Guerrero the only slugger not named Giancarlo Stanton to hit a baseball at least 118.9 mph last year; he also led MLB with eight different balls in play with exit velocities of 115 mph or higher. We know that every added mph of exit velocity, once a hitter gets into triple digits, increases the possibility for damage. So, combine Guerrero’s truly elite power with his better-than-average strikeout and walk rates, and there’s still a ton to like here.

Hope is in ample supply this time of year, so mark this prognosticator as all-in on Guerrero’s fitness improvement and commitment to lift the ball just a little bit more. Vladito will cross 40 homers this year, and we’ll forget that we ever worried about him.
-- Matt Kelly

Cavan Biggio -- 2B, Blue Jays
Key number: 16.5% walk rate

Biggio has played exactly 100 career games and already looks like a veteran, at least as far as plate discipline is concerned. His walk rate was tied for fourth highest among 207 players with at least 400 plate appearances last season, behind only Mike Trout, Yasmani Grandal and Alex Bregman. He had a microscopic 13.5% chase rate, second lowest among players to see at least 750 out-of-zone pitches.

So Biggio knows how to lay off a pitch -- what’s next is figuring out exactly when to swing. His 60.1% swing rate against in-zone pitches was 20th lowest. That could mean some missed opportunities for a guy with an above-average hard-hit rate and an MLB-leading rate of balls hit in the launch angle sweet spot between 8-32 degrees. If he puts the ball in play more, but keeps up that walk rate, Biggio could turn into a valuable on-base machine for the Blue Jays.
-- Sarah Langs

Willie Calhoun -- OF, Rangers
Key number: 36.4% ground-ball rate

If you want to break out in MLB these days, you need to do two things: hit the ball hard, and hit the ball in the air. Calhoun finally started doing both last season, and he popped 21 homers in 83 games with a .524 slugging and .848 OPS. It's time for the 25-year-old to make the leap in 2020. Calhoun was in the top 40% of the league in hard-hit rate, and he was in the lowest 20% of the league in ground-ball rate. That's the right kind of combination.

Now he just needs to make the most of his air contact. Calhoun's popup rate was crazy high -- tied for the highest in the Majors, in fact, at 15.1%. Popups are automatic outs. On the other hand, the guy he was tied with was Edwin Encarnación, who also hit 34 home runs. So popups won't stop you from slugging. And when Calhoun starts turning those popups into fly balls, he's going to be a star.
-- David Adler

Alex Verdugo -- OF, Red Sox
Key number: 91.2% zone-contact rate

Traded as part of the Mookie Betts blockbuster, Verdugo will be responsible for replacing the 2018 AL MVP Award winner in right field, putting immense pressure on him from the get-go. The 23-year-old could be up to the task, however. After a few short stints in the Majors over 2017-18, Verdugo finally received a chance to showcase his skills on a regular basis with Los Angeles last season. In 377 PAs before his campaign was halted by injuries, Verdugo hit .294 with 12 homers, 22 doubles and a 114 OPS+.

Impressively, Verdugo struck out only 13% of the time (MLB average was 23%), and his 91.2% contact rate in the strike zone was the 16th-best mark in MLB (min. 400 in-zone swings). While Verdugo could benefit from hitting fewer ground balls, he has the tools to be a batting-title contender and a doubles machine during his inaugural season in Boston -- once he returns from a stress fracture in his back, that is.
-- Thomas Harrigan

NATIONAL LEAGUE

Brian Anderson -- 3B/OF, Marlins
Key number: 45.7% hard-hit rate

Although he may fly under the radar on a rebuilding Marlins club, Anderson has become an integral member of Miami's core, and he's only getting better at the plate. After a solid 2018 rookie season in which he hit .273/.357/.400 with 11 homers, Anderson improved his isolated power (ISO) by 80 points last year, when he slugged 20 home runs over 520 plate appearances. At the heart of his power surge was an increase in average launch angle from 8.7 degrees to 11.1, and a jump in hard-hit rate from 42.4% to 45.7%, which ranked 35th in MLB among qualified hitters.

Anderson's bat was especially potent after the 2019 All-Star break, when he raised his launch angle to 14.1 degrees and crushed nine homers with a .923 OPS in just 166 PAs. Given the 26-year-old's penchant for producing hard contact, continued elevation may be the key to unlocking his 30-homer potential in 2020.
-- Harrigan

Dansby Swanson -- SS, Braves
57.8% line drive + fly ball rate (29.0% hard-hit LD+FB rate)

There's no reason Dansby shouldn't be great. Well over half of Swanson's batted balls last season were line drives or fly balls -- putting him in the 92nd percentile of MLB in air contact, sandwiched between superstars Trevor Story and Anthony Rendon. Nearly 30% of those line drives and fly balls were hard hit, putting Swanson in the top quarter of the league in hard-hit air contact, right behind Pete Alonso and George Springer. Hard line drives are hits. Hard fly balls are homers. Swanson's got plenty of both. The only thing he doesn't have is the stat sheet to show for it … yet.

Swanson deserved better last year. He underperformed his expected batting average (xBA) by 20 points and his expected slugging percentage by 60 points, despite a 28.7 feet per second sprint speed that put him in the top 15% of MLB (way above the 27 ft/sec league average). Now he just needs to put it all together in one healthy season. Write this down: Swanson is going to have an "all-around star" type of year just like teammates Acuña and Ozzie Albies.
-- Adler

Austin Riley -- 3B, Braves
.588 expected slugging (xSLG) in 1st 35 games

Riley hit seven homers in his first 14 career games, tied for the third most by any player. In his first 35 games, he had 12 homers, 34 RBIs and a .288/.340/.604 line. But then, in his final 45 games, Riley hit .163/.218/.333, as his quality of contact plummeted. He missed time in August and early September with a torn ligament in his right knee, but that downturn began long before, in late June.

There are a few ways to look at this. But the most positive take is that Riley has seen what success looks like at the big league level and can find a way to recapture and build on it in 2020. Riley was MLB Pipeline’s 38th-ranked prospect in the Majors entering 2019, so the promise is certainly there. If he can return to mashing the ball -- with help from some mechanical adjustments -- there’s plenty of reason to believe Riley can help aid Freddie Freeman, Acuña and company in the quest for a third consecutive division title.
-- Langs

Ryan McMahon -- 2B, Rockies
Key number: 91.4 mph average exit velocity

McMahon was one of last year’s quietest 20-plus homer guys, and it feels like there’s room for him to do a lot more. He connected with authority last year, finishing in the 91st percentile in hard-hit rate (47.4%) and the 90th percentile in average exit velocity. (And for those wondering, both figures were nearly identical away from Colorado.) McMahon’s max exit velocity of 112.9 mph was also a top-100 mark, and when he put the ball in the air, he slugged like Mike Trout, Josh Donaldson and Matt Olson.

But obviously McMahon wasn’t Trout, Donaldson or Olson, because he struck out and grounded out too much. McMahon’s chase rate was slightly above average, however, so a slight tweak or two could be all it takes to polish this 25-year-old’s swing. A 35-homer, .850-plus OPS season feels feasible here, especially with 81 of McMahon’s games coming at Coors Field. McMahon’s last three months of 2019 (.252/.331/.500, one HR for every 15 AB) gave us a glimpse of that player.
-- Kelly

Amed Rosario -- SS, Mets
Key number: .291 expected batting average (xBA)

It feels like we’ve been waiting for this for a while now, but Rosario only turned 24 in November, and he has shown considerable improvement since his August 2017 debut. The patience is paying off. Setting aside last summer’s defensive improvement at shortstop, Rosario also raised his offensive numbers across the board, lifting his OPS+ from 88 to an above-average 102. Underlying that was a hard-hit rate that jumped from 32.1% to 39.1% (MLB average was 36.6%) and showed that Rosario isn’t just a slap hitter. It also contributed to a 90th-percentile xBA, backing up last year’s .287 batting average.

More adjustments remain, but Rosario’s combination of contact, pop and wheels (94th-percentile sprint speed) is an intriguing mix heading into 2020.
-- Simon