Fantasy Baseball Prospect Risers - Rookies to Stash and Top Performers for Week 21

August 16, 2026

Jeremy's top fantasy baseball prospect risers, breakouts with big upside for Week 21 of 2026. He analyzes top MLB rookies and call-ups to stash who are surging.

Welcome to the Week 21 edition of the top prospect performers. In this weekly piece, we take a look at some of the top-performing minor leaguers who could matter in fantasy down the road. While some may be promoted more quickly than others, it's important to stay up to date on recent prospect performances so you're ready to add them when they do get the call.

Joshua Baez was featured in this piece last week and finally earned his promotion on Saturday. He wasted no time showing off the tantalizing upside we've waited on for so long, as he had one of the most historic debuts in major league history, homering in each of his first three major league at-bats. If you missed out on Baez, I still recommend stashing Kade Anderson and Walker Jenkins, who were also featured here last week.

While those two remain my stop stashes, there are three other hot prospects to discuss this week. While they aren't as likely to be promoted as Anderson and Jenkins, they all have an outside chance at a promotion and would certainly be worth adding if they do get the call. With only a month and a half left in the season, adding the right prospect at the right time could propel your team through the fantasy playoffs.

Franklin Arias, SS, Boston Red Sox

Red Sox No. 1, Overall No. 3

Franklin Arias signed with the Red Sox out of Venezuela in 2023, looking like one of the best defensive shortstops in his class. That’s certainly a big part of what drives his ranking as the third overall prospect in baseball, but his offensive game has also developed much more rapidly than anyone expected. That started from the moment he started his professional career, but he’s taken an especially big leap in 2026. 

While initially projected to possess 10-15 home run power, his early strides offensively had scouts bumping up his peak projection to 25. Arias wasted no time proving them right, as he already has 23 this season at just 20 years old. While most of it has come at Double-A, the youngster hasn’t missed a beat since moving up to Triple-A on July 25th. 

In 17 games, he’s batting .300 with four home runs and four doubles. On the season, he’s slashing .314/.400/.575 with 23 home runs, 69 RBI, 62 runs, and five stolen bases. His plate discipline is also very advanced for his age, as he's posted a 14.8 % strikeout rate and 10.8% walk rate. 

MLB's No. 3 prospect Franklin Arias is tearing up Triple-A 🔥

In his 15 G with the Worcester Red Sox:
.313/.384/.563
4 2B, 4 HR
17 RBI pic.twitter.com/hkVrPnOSDC

— MLB (@MLB) August 14, 2026

It's very unlikely for a player who is in Double-A at the All-Star break to make his major league debut in the same season, but Arias has a real chance to do so with the Red Sox looking more and more like a playoff team. With Nick Sogard manning second base and Andruw Monasterio at shortstop, it's likely that the prospect would give them the best shot at winning games down the stretch.

They'll be getting a reinforcement soon with Trevor Story starting a rehab assignment, which likely also explains why Arias has been seeing starts at second base recently. It certainly looks like Boston wants him to be prepared to play both infield spots, and the only reason for that is if they expect to promote him at some point soon.

With shortstop being one of the deepest positions in fantasy, it's not worth stashing him unless you play in an extremely deep league. However, he's certainly a name to watch, as he'd be worth adding as a middle infield option if he does get the call.

Verdict: Monitor for promotion

James Tibbs III, OF, Los Angeles Dodgers

Dodgers No. 7, Overall N/A

James Tibbs III was the most talked-about prospect in the early weeks of the season, when he launched seven home runs in the first eight games of the season. While that type of production obviously wasn't sustainable, he ultimately cooled off enough that he never forced the Dodgers' hand to promote him.

However, he's been heating up again as of late, as he's enjoyed a very good month of August so far. The 23-year-old has recorded at least one hit in 11 of his 12 games in August, slashing .378/.500/.622. He has three home runs in the month, and he recently launched two in a game on August 13th.

So nice Tibbs does it twice☄️ pic.twitter.com/2uKmVsbUsT

— Oklahoma City Comets (@OKC_comets) August 14, 2026

This hot-hitting brings his season slash line to .298/.384/.471 with 24 home runs, 88 RBI, 90 runs, and seven stolen bases. The youngster's strikeout rate is a bit high at 22.9%, but he has also walked at a great 16.5% clip. It's been an overall elite offensive season for the outfielder, who probably would have been given a chance in the majors if he were in any other organization.

The Dodgers have no shortage of talent, with Kyle Tucker, Andy Pages, and Teoscar Hernandez in the outfield and Shohei Ohtani filling up the designated hitter slot. It's hard to call up young guys when that's the current state of the roster, but Hernandez has been very disappointing this year, slashing just .249/.314/.400.

It's not out of the realm of possibility that the Dodgers start to take some playing time away from the veteran, and if they do, Tibbs would hopefully be the first in line to step up. This isn't someone worth stashing at this stage of the year, but he remains one of the most impressive hitters in the minors and is worth keeping an eye on, just in case he finally gets his chance.

Verdict: Monitor for promotion

Lazaro Montes, OF, Seattle Mariners

Mariners No. 5, Overall No. 56

Lazaro Montes is also a relative newcomer to Triple-A, being promoted there on July 7th. He didn't let the new level slow him down, as he already has 10 home runs with his new squad. That number has been increasing exponentially as of late, as his homer on Saturday marked three games in a row, bringing his total to seven in August alone.

Lazaro Montes becomes the 2nd Minor Leaguer to reach the 35-HR plateau this season 🚀

Make it 3 straight games with a roundtripper -- this one at 107.6 mph -- for the @Mariners' No. 5 prospect.@RainiersLand | @MsPlayerDev pic.twitter.com/ln1dkgYzBM

— MLB Pipeline (@MLBPipeline) August 15, 2026

For the season, he's slashing .253/.370/.573 with 35 home runs, 87 RBI, 91 runs, and six stolen bases. Clearly, the 21-year-old has a knack for power, as seen by his 112.1 mph max exit velocity, 14.5% barrel rate, and 51.3% hard-hit rate so far at Triple-A. The youngster could be promoted today and instantly become one of the biggest power threats in the majors, although there are some clear weaknesses that are holding him back.

His Z-Contact rate sits at a remarkably terrible clip of 70.3%, as does his 31.4% strikeout rate. If he struggles that much to make contact in Double-A and Triple-A, those concerns would only be amplified at the major league level. To make matters even worse, Seattle is known as one of the most pitching-friendly parks in the league, with many hitters noting that the batter's eye makes it hard to track the ball coming in.

The Mariners also don't need outfield help, especially after acquiring Taylor Ward at the deadline. For those reasons, I'm not expecting Montes to be promoted this season, but you never know. Either way, his recent dominance at Triple-A is worth noting here, as it could put him on the fast track for a spot on the team in 2027.

Verdict: Rising dynasty asset

More Fantasy Baseball Prospects and Rookies