Pitchers and catchers have reported to spring training and the long journey that is the 2021 MLB season has begun. The ongoing pandemic means it will be challenging, but MLB and the MLBPA believe they're up to the task of playing a full season, so let's hope they can do that without interruption. I've missed baseball terribly.

Last year's abbreviated 60-game season brought unexpected performances, good and bad. Who had Kenta Maeda posting the lowest WHIP among qualified starters? What about Javier Baez putting up the third-worst OPS in baseball? Can't say I saw any of that coming. Weird things happen in 60-game samples and the other 102 games weren't available to normalize things.

With that in mind, let's look at five players who had disappointing 2020 seasons and are primed for a rebound in 2021. We're going to ignore players who missed a bunch of time with injuries (like Stephen Strasburg) and instead focus on players who were largely healthy and simply didn't play up to their standards. The players are listed alphabetically.

1. Pete Alonso, Mets

The narrative is so easy it's almost lazy. Hot-shot rookie has a historic debut season, then he struggles through his second year in the big leagues, so bam, sophomore slump. Pitchers adjusted, the player put too much pressure on himself, whatever. We could come up with countless unquantifiable ways to explain a disappointing second season, like Mets slugger Pete Alonso's.

"I wouldn't call it pressure. The uncertainty got to me mentally," Alonso recently told the New York Post's Steve Serby about his struggles last year. "Last season, I failed more than any time in my career, and that simply won't happen again because of my preparation and will to succeed."  

In a lot of ways, Alonso's underwhelming sophomore season mirrored his spectacular rookie campaign. His surface stats didn't match up at all -- Alonso hit .231/.326/.490 in 2020 after putting up a .260/.358/.583 line in 2019 -- but the underlying numbers were almost identical. 

Alonso still hit the snot out of the ball (hard-hit rate is percent of batted balls with at least a 95 mph exit velocity), he didn't strike out more or walk less, and his swing decisions in general were the same. He didn't chase pitches out of the zone more frequently nor did he swing less often at pitches in the zone. 

Under the hood, 2020 Alonso looked a lot like 2019 Alonso. He did trade a few line drives for pop-ups last year, though not enough to explain 29-point drop in batting average and a 93-point drop in slugging percentage. More than anything, Alonso fell victim to the shift in 2020. Opponents more aggressively shifted their defense against him and his production suffered.

When opponents did not shift against Alonso, he was the same basic hitter in 2020 as 2019. He saw considerably more shifts in 2020 though, and he had far less success when he did see the shift. His batting average, both on balls in play and overall (i.e. including homers), plummeted roughly 70 points while his shift rate increased about 50 percent.

Alonso is not an extreme pull hitter -- his 45.1 percent pull rate the last two years was 29th highest among the 128 qualified hitters -- but you don't need to be an extreme pull hitter to have hits taken away by the shift. Teams are relentless and defensive positioning is so good these days. And you know what? Alonso will only see more shifts going forward. It is inevitable.

An adjustment has to be made and I think Alonso is capable of making it. The fact his underlying numbers were unchanged is a good thing -- had Alonso's exit velocity or chase rate declined sharply, it would be a major red flag -- and he has so much power and is so strong that his production shouldn't suffer with a more opposite field approach. The adjustment is not easy, but it can be done.