The offseason positional prospect rankings were launched last week at Rotoballer with a detailed look at the Top 10 catchers. Today, it’s the first base prospects’ turn to be on full display.

There also aren’t a ton of “can’t miss” first base prospects in the pro ranks right now with only one sitting on my “must-have” list right now. But there are still a number of players that could be excellent sources of power for a relatively low acquisition cost -- although there is definitely no future Peter Alfonso to be found here. With that said, the Twins have a sleeper first base prospect that could end up having a breakout season similar to the one Christian Walker had in 2019 for Arizona.

The first basemen rankings are based on the assumption that the Triple-A and MLB baseballs will continue to be juiced in 2020, although many of the players listed have such strong raw power that they’ll produce outstanding power numbers either way.

Top 10 First Base Prospects

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1. Andrew Vaughn, White Sox, 2020 Level: A+

Prior to the 2019 amateur draft, I advocated for Vaughn to go first overall to the Orioles. Instead, Baltimore went with the industry consensus and took college catcher Adley Rutschman while the U of California first baseman was popped third overall by Chicago. Vaughn had a nice pro debut in 2019 despite being pushed overly aggressively by his new club. He played at three levels and topped out in High-A ball. There were some positive indicators with Vaughn’s performance even if he was more good than great. He posted a BB-K of 30-38 in 55 games, which should bode well for his future ability to hit for a strong average. As well, 23 of his 57 hits went for extra bases — including 17 doubles. High doubles totals are usually a strong indicator of future home-run power once players start to lift the ball in the air more consistently and add muscle/strength. There is the potential here for Vaughn to be a .280-.300 hitter with 30 or more home runs.

2. Triston Casas, Red Sox, 2020 Level: A+

The Red Sox have a very thin farm system in terms of potential impact players but Casas is one player that possesses a lot of potential for the future. He could have some additional value for fantasy players if he can earn dual eligibility at both first base and third base once he reaches the Majors. Just 19 years old, this 2018 first-rounder had a solid first full season in the Majors. He averaged just shy of one strikeout per game but displayed plus power by going deep 19 times — good for third in the league behind two players spending their second straight seasons in the league. He also took 58 walks in 120 games, which is encouraging for such a young player. It will be at least two years before Boston fans see Casas in the Majors but he should be well worth the wait.

3. Brent Rooker, Twins, 2020 Level: AAA

It might seem like a bit of a stretch to have Rooker listed this high — and on the first base list at all. He didn’t play a single inning at first base in 2019. Instead, he spent most of his time in left field for the Twins’ Double-A club. However, Rooker spent a good chunk of his junior year of college at first base and also racked up 55 games there in the minors over the first two years of his pro career. As a modest fielding outfielder, it wouldn’t be a shock to see him develop into a dual-position-eligible-player in fantasy baseball once he reaches the Majors. Rooker has massive power potential and has consistently produced outstanding line-drive and isolated slugging rates throughout his three years in pro ball. He likely won’t hit for a ton of average because his strikeout rates are also consistently high (35% at Triple-A in 2019) but he takes a lot of walks, which will be of benefit in leagues that reward walks. Rooker is on my list of sleeper prospects to watch for 2020 — especially if the same baseball is used next year.

4. Evan White, Mariners, 2020 Level: AAA

White is a player that could really benefit from the balls that were used at Triple-A and in the Majors in 2019. A strong offensive performer in college, his success with hitting for average has carried over into pro ball but his power has not developed at expected. White has a strong frame and the potential to hit for pop but his approach and swing have long been geared towards using the whole field and hitting line drives more to than aiming for over-the-fence results. That started to change at Double-A in 2019 when he began to put the ball in the air much more consistently — and he reached a career-high in home runs at 18 despite playing in just 92 games. One thing to keep an eye on, though, is that he also posted a career-low walk rate so we’ll hope for a bounce-back in this area in 2020.

5. Ryan Mountcastle, Orioles, 2020 Level: AAA

Mountcastle moved from third base to first base in 2019. He then also saw time in left field late in the season as Baltimore experimented with different ways to get his bat into the big league lineup. The defensive versatility could be a boon to his fantasy value if he becomes eligible at all three positions. The offensive game, though, is Mountcastle’s claim to fame thanks to his impressive raw power. He slugged 25 home runs in just 127 games at Triple-A in 2019 while also adding another 35 doubles. A .300 batting average is likely not in the cards for Mountcastle, despite his 2019 output, as he relied heavily on his Batting Average on Balls in Play (BABIP) which was an unsustainable .370. His BB-K of 24-130 also leaves a lot to be desired.

6. Bobby Bradley, Indians, 2020 Level: AAA

Bradley is similar to Mountcastle but with a little less feel for the hit tool but better patience. If your fantasy league counts walks then you probably want to flip the two players in the rankings. Bradley’s power output has been extremely consistent throughout his pro career and he’s hit fewer than 27 home runs in a season only once over the past six seasons. If he can make enough contact against big league pitchers, Bradley has 30 home run potential but it would likely come with 180-200 strikeouts. The young first baseman doesn’t have a clear path to playing time in the Majors for 2020 with Franmil Reyes and Carlos Santana (who has a contract option) possibly acting as roadblocks.

7. Seth Beer, Diamondbacks, 2020 Level: AA

Selected by the Astros in the first round in 2018, Beer reached Double-A in his first full season — and was also a key piece in the 2019 Zack Greinke trade with Arizona. He went deep 26 times while playing for three teams at two different levels but projects as more of a good-not-great future big leaguer. He’s been a solid statistical performer to date but he lacks athleticism and premium bat speed so there is concern about his ability to consistent tap into his raw power against MLB pitching.

8. Grant Lavigne, Rockies, 2020 Level: A+

The list drops off a bit here. Lavigne is coming off a disappointing season. Drafted 42nd overall in 2018, the hulking teenaged first baseman struggled to tap into his raw power potential and just 26 of his 104 hits went for extra-base hits. He hit far too many balls on the ground and will likely need to adjust his swing to embrace the fly-ball revolution. Lavigne had a lot of swing-and-miss to his game (129 strikeouts in 126 games) but also showed promising patience (68 walks). If he can consistently tap into his raw power, the young hitter is in the right organization to make a real impact with that tool at the big league level.

9. Lewin Diaz, Marlins, 2020 Level: AA

Diaz started to tap into his considerable potential in 2019. After hitting a career-high 12 home runs in 2018, the young hitter more than doubled his output in 2019 with 27. The Twins prospect attracted the attention of the Marlins and he was acquired in a trade deadline deal. Diaz really struggled after the trade and it’s worth noting that Miami is not as strong at player development as Minnesota. The young left-handed hitter really struggles against same-side pitching so he has a fair bit of work to do to avoid a future platoon role.

10. Michael Toglia, Rockies, 2020 Level: A+

Drafted in the first round out of UCLA in 2019, Toglia may not provide much of a batting average as a pro but he’s shown the ability to produce strong power numbers with wood bats as an amateur — and also during his brief pro debut. He went deep nine times in 41 games in the short-season A-ball league after signing his first pro contract. And while there is some swing-and-miss to his game, he’s also shown a willingness to take a walk and was issued 28 free passes in his debut. Colorado could open 2020 with two top first base prospects in advanced A-ball although Toglia could spend more of his time in the corner outfield, which has the potential to improve his fantasy value.

Just Missed: Bobby Dalbec (Red Sox) and Gavin Sheets (White Sox)