Fantasy Baseball Waiver Wire Analysis: Buyer Beware for Week 10? (2025)

May 31, 2025

Michael's fantasy baseball waiver wire analysis for Week 10 (2025), and whether to buy into MLB hitters and pitchers. Should you avoid these popular names?

Welcome back to another installment in our weekly Buyer Beware waiver wire series.

Incredibly, it’s Week 10 already. There’s an old saying about aging and time: the days are long but the years are short. That’s how this baseball season feels for yours truly.

This week, we examine two prospects who were recently promoted to the big leagues and a former closer who reclaimed the ninth-inning role. Should you spend precious FAAB dollars on this trio? Let’s get to the names!

• Fantasy baseball draft kit
• Fantasy baseball rankings
• Team Sync platform and Draft Assistant
• Fantasy baseball mock draft simulator
• Fantasy baseball draft cheat sheets
• Fantasy baseball closer depth charts
• Fantasy baseball prospects

Marcelo Mayer, SS, Boston Red Sox

26% rostered

Mayer is one of Boston’s “Big Three” prospects and was called up last week to some fanfare. The natural shortstop has played every day since, with most of his starts coming at third base.

Mayer is a consensus top 20 overall prospect. We know he is well-regarded generally but is he a great prospect for fantasy purposes?

Here is a Baseball Savant-style player page for Mayer’s Triple-A performance this season, courtesy of Thomas Nestico (@TJStats on X):

Mayer might profile best in points and OBP-based formats. In the minors, he walked at a nearly double-digit rate, and he has reduced the strikeouts, which fell to a sub-20% rate the past two seasons from the 24% range earlier in his pro career.

We are somewhat skeptical of Mayer’s impact in category-based leagues because the strengths driving his real-world value are defense and 60-grade power. A 106.3 90th percentile EV is definitely plus (104.2 was the MLB league average in 2024).

However, that power may be muted by his home park. Fenway is a great place for hits overall, but Statcast ranks it 20th in home run park factor (91) for lefties like Mayer. While he hits the ball fairly hard and pulls it well in general, he only pulls it in the air at an average rate.

FanGraphs rates Mayer’s current hit tool as below average (30 present/40 future grade), and his FanGraphs prospect report notes that Mayer struggled to hit breaking balls in the upper minors. Hence, his batting average may be a true negative given the quality of major league pitching.

Mayer may chip in a handful of stolen bases using his good, but not elite, speed (75th percentile sprint speed). His career-high steals total was 17 back in 2022, although last season he did nab 13 swipes in just 77 games. But he only has two steals on two attempts across 49 games in the minors and majors this year.

The projections systems paint Mayer as a solid, if unspectacular, offensive player. The ATC projections -- available on RotoBaller  -- call for a .256 average with eight homers and five steals in about half a season (337 plate appearances).

Here is his Steamer 600 projection, which estimates production over 600 plate appearances: .246 average, 12 home runs, and 11 steals.

We all get excited when a top prospect gets the call to the big leagues. Mayer should have a decent leash to play regularly. But before spending big FAAB dollars or dropping a useful player to add Mayer, proceed cautiously because he is unlikely to provide a high-ceiling return for fantasy purposes.

Alejandro Osuna, OF, Texas Rangers

2% rostered

The Rangers called up Osuna last weekend, and he has started in left field against every righty starter Texas has faced since. The move was preceded by Joc Pederson and Evan Carter both hitting the injured list last week.

A solid prospect in the lower minors, Osuna leaped last season by hitting .297 with 18 homers and 17 steals across stops in High-A and Double-A. He reached Triple-A this year and showed strong plate discipline with nine walks to eight strikeouts.

In his first week with the big club, Osuna has continued to display good plate patience with three walks to three strikeouts through Friday. He had not yet homered or stolen a base.

There are two reasons to pump the brakes on Osuna. First, he offers limited upside, especially in traditional roto leagues. Similar to Mayer, he may be more useful in points and OBP-based formats.

Osuna’s power is likely limited, as he was given a 50 grade, per MLB Pipeline (50 is average on the 20-80 scouting scale).

Statcast’s bat speed metric becomes reliable very quickly, and Osuna’s 69.3 miles per hour swing ranks in the 15th percentile. That’s in the range of Gavin Lux and Tyler Fitzgerald.

Osuna has good speed, but he has been a relatively inefficient base stealer in the minors (17 for 23 last season). That 74 percent success rate is almost 6 percent below the MLB league average.

The other reason for caution here is playing time. While Pederson will miss at least six weeks, Carter has already begun a rehab assignment and should return soon.

The Rangers could cycle Osuna and Carter between the outfield and DH against right-handed pitchers. But Osuna won’t face lefties, and the team has not confirmed whether he will continue to play regularly when Carter is back in the fold.

Osuna has intriguing potential, but for now, he is only a deep league play. Given the lack of certainty around his role, we would keep any bids to just one or two FAAB dollars (out of a $1,000 starting budget).

Camilo Doval, RP, San Francisco Giants

48% rostered

Doval was named the Giants closer by manager Bob Melvin on Wednesday. Finding a named closer on the wire is rare, let alone one with Doval’s record of success, so clearly, he needs to be added to any league that rewards saves or saves-plus-holds.

Doval is a repeat guest on Buyer Beware (Week 7). As we noted then, this is not the elite 2023 version of Doval despite an outstanding 1.09 ERA. He is getting quite fortunate in terms of hitting luck, and his velocity and whiff rates have declined from his peak a couple of years ago.

Doval’s cutter averaged 99.8 miles per hour in 2023; now it’s 98.1. His sinker is also down, from 97.9 to 95.5. These reductions haven’t granted him any new level of control, either. His 9.3% walk rate is identical to two seasons ago. It’s an improvement on last year, but the lower velocity has also curbed his swing-and-miss.

Doval’s overall strikeout rate is down 7.7% from 2023. The current 23.3% rate is the league average for a reliever (22.5%).

He is getting fewer whiffs on all pitch types:

The whiff rate on Doval’s cutter, his primary fastball, has been almost cut in half to 15.8% from 30.4%. His slider missed bats at an elite 49.3% rate in 2023; now it is merely good at 38.2%.

The pitching models confirm that Doval is diminished now. His 106 Stuff+ is down 10 points from two seasons ago.

Meanwhile, Doval is throwing more strikes (zone rate up 2 percent), and batters are making more contact (zone contact up 4 percent). Yet, somehow, he’s allowing a .158 batting average on balls in play. It was .305 for his career entering this season.

He also hasn’t allowed a single home run! That probably isn’t sustainable.

This isn’t to say Doval will be bad. He is doing many things well, including minimizing hard contact (87.4 average exit velocity, 3.5% barrel rate). But only six relievers maintained a sub-.200 BABIP last season. Only two did not allow a home run. Go get him, but be prepared for some degree of regression.

More Fantasy Baseball Analysis