The 2019 season saw a significant number of rookie hitters debut with great success. But Major League Baseball’s history is littered with strong freshman debuts followed by disappointing sophomore campaigns. In other words, successful rookie seasons do not guarantee all-star careers or even another good performance.

We can look back at 2016 for some examples of rookie land mines. Cleveland outfielder Tyler Naquin played in 116 games and produced a 133 wRC+, which means he was 33% better than a league-average MLB hitter. But there were also two major red flags. The good-not-great runner produced a .411 BABIP. He also struck out at a rate of almost 32%. From there, Naquin spent two years trying to find his footing at the big league level. He played just 19 games at the MLB level in his sophomore season and did not perform well with the bat. He played more in 2018 and 2019 but has struggled to create average offensive production.

Keon Broxton was another player from 2016 that teased us with his potential. He stole 23 bases in 75 games and also produced a walk rate of almost 15%. But the warning signs were there: a .373 BABIP and a strikeout rate of 36%. Broxton had more success than Naquin in his sophomore season and actually followed up with a 20-20 season but the strikeout rate increased again. Over the last two years, he’s been trusted very little at the plate and has been used mostly as a defensive replacement and pinch-runner. While the following three players we discuss were all more highly-regarded prospects than Naquin or Broxton, their prospect status in no way protects them against taking a step back this year. So, let’s take a look at three 2019 rookie hitters that are at risk of seeing some regression during the 2020 season.

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You don’t want to hear it, but there is some risk for regression with Tatis Jr. as the explosive infielder enters his sophomore season. Because he hits the ball really hard and has good speed, he’s the type of player that can produce — and sustain — strong BABIPs. But a .410 BABIP isn’t sustainable for even the best players in the world. Mike Trout managed to sit around .380 for his first two full seasons but stayed closer to an average of .345-.350 over the next five seasons. And that’s around the same rate Tatis Jr. produced in the minors. That potential reduction significantly lets the air out of the young shortstop’s batting average and on-base percentage, which were at impressive levels of .317 and .379 in 2019. His 2019 xBA of .259 supports a potential regression for 2020 unless he makes adjustments.

Tatis Jr.'s xSLG of .490 in 2019 also indicates some potential regression with his power. But his well-above-average barrel rate of 13.2% and slightly-above-average exit velocity of 89.6 mph suggest he's well-positioned to create more sustainable power if he improves upon his 6.9-degree launch angle, which is well below average. Tatis Jr. also has very good speed, although he's not as advanced a base runner as Trout was early on in his career. In his first three MLB seasons, the Angels' superstar had a success rate of more than 87% in more than 100 attempts. Tatis Jr. is closer to 70% in almost 100 attempts over the last three years (combining the majors and minors).

While the rookie’s season was impressive, he has yet to prove he’s the next Mike Trout, a player capable of being an explosive offensive threat in just about every conceivable fantasy category. Tatis Jr. will very likely produce Tout-like power with an increased launch angle as he matures as a hitter, but consistently-strong performances in categories such as batting average, on-base percentage, and steals are not guaranteed. This is a player that currently has an ADP of 21, so a lot of fantasy managers are heavily counting on him to perform as well or better in 2020.

Hiura is an interesting player. It’s always been a foregone conclusion that he would hit well at the MLB level. He was selected ninth overall in the 2017 amateur draft after hitting .442 as a college junior and then posted a .303 batting average while swiftly making his way through the minors. But no one expected the modestly-sized second baseman to hit 38 home runs in 2019 while splitting the year between Triple-A and the majors. With metal bats in college, his best home run output was eight. In the minors, he managed 13 in 2018. But then Hiura met the juiced ball in Triple-A and it was a match made in heaven with his massive line-drive rates. And when the young middle infielder reached the majors, he made some adjustments and went from being more of a ground-ball hitter to more of a fly-ball hitter.

Hiura is another player that consistently produces good BABIP rates because he has solid foot speed and regularly stings the ball, as witnessed by his 13.9% barrel rate and 50% hard-hit ball rate (which was among the Top 3% in the league). But the .402 BABIP he produced in 84 games is not sustainable. Neither is the .389 BABIP from Triple-A. The strikeout rate of nearly 31% is also a massive warning sign for a player who has made his name from being a “plus hitter.” As Hiura evolves his game to become more of a power hitter, his batting average is going to suffer and his xBA of .266 supports this notion; players that strike out 28-30% of the time just don’t hit .300 consistently. Of the 101 big league hitters in 2019 with at least 250 at-bats and a strikeout rate of 25% or more, only five players hit .300 or more: Hiura, Tatis Jr., David Dahl, Yordan Alvarez, and Nelson Cruz. Only Cruz played a full season.

This player who hit .313 with 38 home runs between Triple-A and the majors is not likely to return in 2020. We could end up with a .300 hitter who blasts 20 home runs and steals 10-12 bases, or we could end up with a .260 hitter with more than 30 home runs and 10-12 stolen bases. While it’s also not clear what direction Kiura will move toward going forward, his well-above-average launch angle of 16 degrees did not just happen by accident. Both versions of Kiura would be valuable fantasy contributors, but there is a very low chance that he’ll replicate his almost unheard of results from 2019. With an ADP of right around 54, he's being drafted higher than some more proven power sources like Giancarlo Stanton (ADP 63), which seems aggressive.

Lowe was trending for a possible 30-homer season before injuries struck and limited him to just 82 games in 2019. He finished the season with 17 home runs and a .270 batting average. His offensive results were considered 25% better than league average with his 125 wRC+. But he was also lucky with a .377 BABIP. A strikeout rate of nearly 35% is also a cause for concern as we look towards 2020. If Lowe continues on his current path and has his BABIP normalize, then he becomes a source of continued power but a lower batting average; his 2019 xBA was only .238.

Like Hiura though, Lowe hits the ball really hard and produced a 46% hard-hit ball rate in 2019, as well as a 16% barrel rate so he could sustain higher-than-average BABIPs at least until his average foot speed loses a step or two. And even if the average does dip, the power should continue to play with a very steep launch angle of 18.7 degrees to go with the consistently hard-hit balls. The key for him to realize his full potential will be to cut down on the strikeouts and get down more in the 22-25% range he enjoyed in the upper levels of the minors without sacrificing the power output seen in 2019.

Lowe also has some additional value in on-base leagues because he’s always posted strong (double-digit) walk rates in the minors. The on-base acumen could also help him post a healthy number of runs, although that category also relies on the hitters around him. One other benefit is that Lowe can play multiple positions. When all is said and done, he's likely a useful fantasy player but one saved for a later-round acquisition given the limited number of offensive fantasy categories he's a safe bet to contribute to at this point. His ADP is currently 195, which is baking in some regression from 2019, and seems about right.