3 Impact Fantasy Baseball Prospects To Stash - Jac Caglianone, Matt Shaw, Marcelo Mayer

June 4, 2025

Three top fantasy baseball prospects - Jac Caglianone, Matt Shaw, Marcelo Mayer - who can make big impacts. These MLB prospects are waiver wire pickups or stashes.

It's not surprising that we are starting to see more and more prospects get called up. We are at the point of the season when teams are dealing with injuries and potentially need a spark on offense. Prospects like Nick Kurtz, Dalton Rushing, Coby Mayo, and Cade Horton are some of the biggest names to be promoted this year.

Three more prospects to add to that list are Kansas City Royals first baseman Jac Caglianone, Chicago Cubs third baseman Matt Shaw, and Boston Red Sox shortstop Marcelo Mayer. All three youngsters are currently in the majors and have the potential to be solid fantasy options in Year 1.

So, should fantasy managers be adding Caglianone, Shaw, and Mayer in fantasy? Let's dive in and see if these three prospects should be grabbed off the waiver wire before it's too late.

Jac Caglianone, 1B, Kansas City Royals

Current Level: Kansas City Royals
Availability: 64% rostered
2025 MiLB stats: 50 G, .322/.389/.593, 15 HRs, 56 RBI, 41 R, 2 SB

Kansas City's top prospect has quickly risen up the minor league ranks since being drafted sixth overall in the 2024 MLB Draft. Caglianone played just 29 games at High-A in 2024 before starting the 2025 season at Double-A Northwest Arkansas. In Double-A, the left-handed slugger hit .322 with nine home runs and 43 RBI in his first 38 games.

Those numbers earned Caglianone a promotion to Triple-A Omaha on May 20. Unsurprisingly, the 22-year-old continued his strong season in Omaha by slashing .319/.370/.723 with six home runs and 13 RBI in his first 12 games. That left the Royals no choice but to promote him to the major league roster. That's exactly what the team did on June 3.

Jac Caglianone played his first Triple-A game on May 20th.

In just TWELVE games, he hit .319 with 6 homers and a 1.093 OPS 😳

Today, he'll be with the big league club. That's dominance 👏 pic.twitter.com/761uhOUzVX

— MLB (@MLB) June 3, 2025

After being drafted just 11 months earlier, Caglianone made his MLB debut on Tuesday against the St. Louis Cardinals. Although MLB Pipeline's No. 10 overall prospect went hitless in his debut (0-for-5), there are some things to be encouraged by. He didn't strike out in any of those plate appearances and had four hit balls over 96 mph.

Caglianone also had a hit taken away from him in the second inning. He belted a ball into the right-center gap, but Cardinals center fielder Victor Scott II made a nice grab to rob him of a hit. That ball was hit 98.4 mph off the bat and had an expected .330 batting average. So, he was a bit unlucky at the plate in his MLB debut.

If he is still somehow available in your league, he should be picked up immediately. Caglianone should be rostered in almost every format, considering his above-average power at the plate. He hit 15 home runs and drove in 56 runs across just 50 games between Double-A and Triple-A this season.

Matt Shaw, 3B, Chicago Cubs

Current Level: Chicago Cubs
Availability: 51% rostered
2025 AAA stats: 24 G, .286/.409/.560, 6 HRs, 14 RBI, 22 R, 5 SB
2024 MLB stats: 31 G, .238/.328/.333, 1 HR, 7 RBI, 18 R, 5 SB

Everyone expected Shaw to make the Cubs' Opening Day roster. Chicago had a clear hole to fill at third base, and the team's top prospect showed a ton of promise in his first two minor league seasons. He hit .357 with eight home runs, 28 RBI, and 15 stolen bases in 38 games in 2023 and batted .284 with 21 home runs, 71 RBI, and 31 stolen bases across 121 games in 2024.

That made Shaw a sleeper target later in 2025 fantasy drafts. However, MLB Pipeline's No. 18 overall prospect got off to a brutal start with the Cubs. He hit just .172 with one home run, three RBI, and 18 strikeouts in his first 18 games. Those slow start led to Chicago optioning its top prospect down to Triple-A to work on a few things.

The good news is that Shaw's time in Triple-A seemed to work out well for him. He slashed .286/.409/.560 with six home runs and 14 RBI across 24 games with the Iowa Cubs before being promoted to the major league roster on May 19. Since being called back up, the Cubs third baseman has been much more consistent at the plate.

Matt Shaw is the first @Cubs rookie 23 years or younger with a walk-off hit since Kris Bryant in 2015 😏 pic.twitter.com/1k5a81wqe3

— Marquee Sports Network (@WatchMarquee) May 28, 2025

In his second major league stint, Shaw is batting .319 with six doubles, four RBI, and five stolen bases across 13 games. It has been nice to see the 23-year-old bounce back after a rough start to the year. More importantly, he is becoming a solid fantasy option for those in roto leagues.

So, he is worth an add in most 12-plus team leagues in Week 10 of the fantasy baseball season. Shaw has shown his all-around potential in recent weeks, and he's someone who could steal close to 20 bases in 2025. That makes him a nice target, especially since he could hit for a solid average, steal bases, and score plenty of runs in this elite Cubs offense.

Marcelo Mayer, SS, Boston Red Sox

Level: Boston Red Sox
Availability: 20% rostered
2025 AAA stats: 43 G, .271/.347/.471, 9 HRs, 43 RBI, 31 R, 2 SB
2025 MLB stats: 8 G, .188/.257/.250, 6 H, 2 2B, 2 R, 2 BB, 10 K

When star third baseman Alex Bregman went down with a significant quad injury, the Red Sox decided to call up one of their top prospects on May 24. Mayer had been tearing it up at Triple-A to start the season and was definitely deserving of a promotion. MLB Pipeline's No. 8 overall prospect hit .271 with nine home runs and 43 RBI across 43 games.

That strong start comes after Mayer posted solid all-around numbers in his 2024 minor league campaign. He slashed .307/.370/.480 with eight home runs, 38 RBI, and 13 stolen bases in 77 games at Double-A Portland last year. As a result, the 22-year-old had the potential to be a solid fantasy option right away in the pros.

Unfortunately, Mayer has struggled in his first few games since being called up. He has just six hits across 32 at-bats (.188 batting average) to begin his major league career and has struck out in 10 of those plate appearances. On top of that, his expected batting average (.243), squared-up rate (19%), whiff rate (32.4%), and walk rate (6.3%) all rank poorly.

.@jcmccaffrey on Marcelo Mayer's smooth transition to the Bigs ⬇️

"The maturity, that was something that always stood out... now he's here, and he's kind of taking it in strides."@TomCaron pic.twitter.com/S9Li57G9cu

— NESN (@NESN) June 4, 2025

Therefore, some fantasy managers might be concerned with Mayer's long-term fantasy outlook. There haven't been many positives from him so far, and the 22-year-old is striking out at an extremely high rate (31.3% strikeout rate). That makes him only an add in deeper leagues or AL-only formats in Week 10 of the fantasy baseball season.

While fantasy managers should expect Mayer to eventually pick things up offensively, he might not be a fantasy star in his first season. He has the chance to hit for a solid average and steal double-digit bases. However, the Red Sox infielder won't hit for much power and likely won't drive in many runs toward the bottom of that Boston lineup.

In points leagues, Mayer should also only be added in deeper formats. There's no doubt that the top-10 prospect will post better numbers moving forward, but he doesn't really warrant an add in most leagues right now. There are better prospects to add/stash, including Caglianone, Shaw, Bubba Chandler, and Andrew Painter.

More Fantasy Baseball Prospects and Rookies