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MLB and the Baseball Writers Association of America announced the 2020 Rookies of the Year on Monday night. Mariners slugger Kyle Lewis was the unanimous winner in the American League. Brewers reliever Devin Williams won the honor in the National League.

These days rookies are making an immediate impact moreso than at any point in baseball history. They're not just playing well for rebuilding teams. They're impacting postseason races, like Robert and Cronenworth. MLB clubs are very good (and getting better) at player development, and these kids are ready to produce as soon as they arrive in the big leagues. It's awfully impressive. 

Earlier this year MLB adjusted the rookie eligibility criteria for the short 60-game season. The 50 innings or 130 at-bats thresholds remain the same, but the service time criteria has changed. Typically players who spend 45 days on the active roster outside the September roster expansion period exhaust rookie status. This year, September counts toward the 45-day limit.

The rule change means players who spent the entire 2020 season on their team's MLB roster will not retain rookie status next year, as they would have under the old rules. Also, MLB has ruled that whoever wins Rookie of the Year this year can not win it again next year, even if they retain rookie eligibility. A two-time Rookie of the Year winner would've been something else, huh?

Because there is never a bad time to look to the future, here are five early 2021 Rookie of the Year candidates for each league, listed alphabetically. If you watched the postseason at all, you saw more than a few of these players in action.

American League

Yes, Randy Arozarena will still be considered a rookie in 2021. He has 81 career regular season at-bats -- postseason at-bats do not count toward rookie eligibility -- and the Rays did not call him up from the alternate site until Aug. 30, so he hasn't exceeded the service time threshold. Handsome Randy was named ALCS MVP this year and he holds the record for hits (29), home runs (10), and total bases (64) in a single postseason, and next year he'll shoot for Rookie of the Year. I wouldn't expect Arozarena to hit like he did in the postseason all next season, no one does that, but we know he will be in Tampa's lineup all season long, and playing time is often half the battle in the Rookie of the Year race.

If not for a separated shoulder, White Sox second baseman Nick Madrigal would've exceeded the rookie limits this past season. Instead, he missed about three weeks and finished with 103 at-bats. Madrigal authored a .340/.376/.369 batting line with only seven strikeouts -- seven strikeouts! -- in those 103 at-bats. Maybe he won't hit .340 all year, but he's a contact machine, and the high-powered White Sox offense will give him plenty of opportunities to score runs and drive in runs. That plus a few steals and strong defense at second base could help Madrigal overcome a lack of power come Rookie of the Year voting time.

A forearm injury limited Triston McKenzie to 90 2/3 innings in 2018 and a back injury kept him off the mound entirely in 2019, but he was healthy in 2020, and after some time at the alternate site, he joined Cleveland and threw 33 1/3 innings with a 3.24 ERA. He struck out 42 and walked nine. Just a remarkable story. The Mike Clevinger trade potentially opened a rotation spot for McKenzie next year -- Cleveland could move Carlos Carrasco to clear salary this offseason as well -- though it's very likely he will be on some sort of workload limit next season. That could cut into his Rookie of the Year candidacy.

Orioles outfielder Ryan Mountcastle very likely received Rookie of the Year support this year, even if only a dinky third-place vote for two. He hit .333/.386/.492 with five home runs this past season, but because he had only 126 at-bats, he will be rookie eligible again next year. He's poised to join the exclusive club of players who received Rookie of the Year votes in multiple years. Gregg Jefferies is the most recent to do it (1988 and 1989). Mountcastle played more than well enough to be in the Opening Day lineup next year and is home ballpark is hitter friendly, which will help his cause.

Nate Pearson
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Does the Wild Card Series play out differently with a healthy Nate Pearson? Eh, probably not, but the Blue Jays lost their prized young flamethrower to elbow tightness in late August, and by the time he returned in late September, he had to be limited to relief work. The injury also limited Pearson to only 18 innings, well short of the rookie threshold. He may have to compete for a rotation spot in Spring Training but figures to spend most of the 2021 season in the big leagues one way or another. Walks and homers will be the biggest obstacles during his pursuit of the league's top rookie honor.

Other candidates: IF Bobby Dalbec, Red Sox; RHP Dane Dunning, White Sox; RHP Deivi Garcia, Yankees; OF Alex Kirilloff, Twins; RHP Michael Kopech, White Sox; RHP Casey Mize, Tigers

National League

Braves righty Ian Anderson will still be rookie eligible in 2021. Getty Images

Braves righty Ian Anderson has thrown 51 innings in the big leagues, but because 18 2/3 of them were in the postseason, he retains rookie eligibility going into 2021. Anderson was marvelous for Atlanta this season -- he allowed nine earned runs in those 51 innings -- and could very well be the team's No. 2 starter going into next year depending on Mike Soroka's recovery from his Achilles injury. There will be some workload considerations here (Anderson has never thrown more than 135 2/3 innings in a season), but Anderson got a great head start on his 2021 Rookie of the Year campaign in 2020.

Although his 2020 MLB debut was a bit bumpy, Cardinals outfielder Dylan Carlson was excellent following his September demotion to the alternate site, going 10 for 36 (.278) with four doubles and two homers in his final 12 regular season games. He then batted cleanup in the team's three postseason games. Carlson fell 20 at-bats short of the rookie threshold and is still one of the game's best and most talented prospects. The smart money is on St. Louis giving him a full-time lineup spot right from the get-go next season. Playing time shouldn't be an issue.

Ke'Bryan Hayes
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Fun fact: Ke'Bryan Hayes led rookie position players with 1.7 WAR this past season. He hit .376/.442/.682 in 24 games following his September call-up and also played Gold Glove-caliber defense at the hot corner, which was his calling card coming up through the minors. It's a small sample, but Hayes was a member of the ultra-exclusive 90/90 club this year (90 percent contact rate on pitches in the strike zone and a 90 mph average exit velocity), which portends very well going forward. Only a handful of guys do that each year and they tend to be stars or players on the cusp of stardom.

Adam Duvall's oblique injury pushed Cristian Pache into Atlanta's everyday lineup in the postseason and he slugged a homer with three walks and only four strikeouts in seven games. He held his own despite limited regular season action (four at-bats) and spending most of the season playing glorified sandlot games at the alternate site. Pache is a defensive wizard in center field, legitimately one of the best defenders in the game already, and that will give him a nice WAR boost next season, assuming he displaces Ender Inciarte to get the job. The playing time is not guaranteed here but Pache is an awfully impressive player.

Even if you include postseason innings, Marlins righty Sixto Sanchez still falls short of the 50-inning rookie threshold (39 regular season and eight postseason). He limped to the finish a bit but I wouldn't use that to discount his Rookie of the Year candidacy in 2021. Sanchez has top one percent stuff and he'll have a rotation spot on Opening Day. Few rookie pitchers have this much raw ability and a guaranteed rotation spot. Sixto has had some issues when he's faced teams the second time, so that will require an adjustment, otherwise all the tools are there for immediate success.

Other candidates: C Joey Bart, Giants; SS Jazz Chisholm, Marlins; LHP MacKenzie Gore, Padres; RHP Josiah Gray, Dodgers; RHP Spencer Howard, Phillies; LHP Brailyn Marquez, Cubs