Dynasty Fantasy Baseball Risers, Fallers, and Buys/Sells - Chris Clegg's Outlooks for Week 9

Chris Clegg's dynasty fantasy baseball buy lows, sell highs, and MLB news for Week 9 (2025). Notable prospects debuts and dynasty risers/fallers including..

Welcome back, RotoBallers, to my dynasty fantasy baseball risers, fallers, and buys/sells for Week 9 of the 2025 MLB season. As May comes to a close, sample sizes have begun to stabilize, and there is less noise in the samples. Prospects are getting the call to majors, and there is plenty to discuss.

Today's dynasty article will look at recent prospect call-ups like Marcelo Mayer, Dalton Rushing, and Alejandro Osuna, along with several other dynasty-related news items. This bi-weekly series will examine various prospects and dynasty news and discuss fantasy implications. If you enjoy dynasty baseball, you know it is a fast-paced game. Keeping up with current events can help you stay ahead of your league mates.

Call-ups, trends, and buying and selling players are all just small pieces to help you stay ahead. So, that's what we will do in this article each week: break down everything you need to know to be successful in dynasty. At the end of the day, we all want to build a dynasty team that sustains and lasts for the long haul. I am here to help you do so. So, what do you need to know for dynasty leagues in Week 9 of the 2025 season? Let's dive in.

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Recent MLB Prospect Call-Ups

Marcelo Mayer got the call to join the Red Sox, but had to be driven to the stadium because he had lost his car keys. Apparently, his car has sat at Polar Park for over two weeks due to the lost keys.

A fun side note, but what does Mayer bring to the table? He has a strong frame for a shortstop with smooth actions in the field. At the plate, he shows a simple setup and a direct path to the ball with a solid feel for the barrel. His quick hands help generate plenty of bat speed, which has taken steps forward each season.

For a third straight season, his power progressed. Mayer’s 90th percentile exit velocity jumped to 106.5 mph, and he maxed out at 115 last year. Launch angles have taken a big step forward this year, allowing him to get to more home run power. Mayer had nine home runs in Triple-A in 193 plate appearances.

The contact skills also took a big leap this year. His in-zone contact rate jumped to 87 percent, and the overall contact rate rose to 77 percent. The approach is good, and Mayer seems primed to be successful in his MLB debut. The biggest question is how he will fare against good breaking balls.

Dalton Rushing has hit and hit some more since being drafted by the Dodgers in the second round of the 2022 draft. Before his call-up to join the Dodgers in Los Angeles, Rushing owned a career minor league slash line of .277/.412/.519 with 54 home runs and 55 doubles in 1,149 plate appearances.

In 2025, Rushing spent the season in Triple-A, where he put together a slash of .308/.424/.514 with five home runs in 132 plate appearances. While he has played inconsistently in the majors, he has shown the ability to hit the ball quite hard.

It is the combination of skills that makes Rushing one of the most well-rounded hitting prospects in baseball. He makes contact, rarely chases, hits the ball hard, and hits it at ideal angles. The barrel rates are elite for Rushing, thanks to a 90th percentile exit velocity of 106 mph, which already puts him in the plus territory of MLB hitters.

Considering the low ground-ball rates, Rushing put the ball in the air over 60 percent of the time, leading to ideal launch angles and many barrels.

The contact skills with Rushing are also impressive. With an overall mark north of 79 percent, the number jumps north of 85 percent in-zone. He knows the strike zone well and picks up spin. He chased less than 18 percent of the time out of the zone. Inconsistent playing time in Los Angeles is the biggest concern here.

Alejandro Osuna just hits. A player I have seen live quite often, I have seen Osuna hit for the cycle as well as hit some impressive home runs. Splitting time between Double-A and Triple-A in 2025, Osuna slashed .279/.386/.416 with two home runs and nine stolen bases.

Osuna sprays line drives to all fields well, but he also can get loft and get to the pull side home run power. The 90th percentile exit velocity being north of 105 mph is pretty impressive when you pair it with the fact that 55 percent of batted balls went in the air.

The contact skills are good. Osuna ran an overall mark of 89 percent between both levels, with a chase rate in the low 20 percent range. His in-zone contact rate has been north of 90 percent.

While being smaller in stature, Osuna runs well and puts 100 percent effort into every play. He is passionate and plays bigger than his 5-foot-9 frame. He makes a ton of contact, which gives him a high floor to succeed right away in the majors.

Dynasty Trends: Swing Path and Attack Angle Metrics

Baseball Savant got new stats, so, of course, we need to talk about them. One thing I love about baseball is how in-depth we can research it. Some may say it is too much, but I think if there is something to be learned about player evaluation and we can have a deeper understanding, it is a good thing.

Here is how Baseball Savant defines its new metrics:

"Attack Angle and Attack Direction both pertain to the direction in which the sweet spot of the bat is traveling as it impacts the ball. Attack Angle measures the vertical component of that direction, as compared to the ground, while Attack Direction measures the horizontal component, in degrees towards the "PULL" or "OPPO" direction, as compared to an imaginary line directed from home plate to straightaway center field."

• Contacting the ball with an Attack Angle between 5-20° is considered "ideal."

"Swing Path Tilt measures the angular orientation of the "plane" of the swing, as compared to the ground, defined by the path of the bat in the 40 ms prior to contact, which approximates a slice of a flat disc in shape. A higher angle is a "steeper" swing (further from horizontal) and a lower angle is a "flatter" swing (closer to horizontal)."

Highest Ideal Attack Angle%

Lowest Ideal Attack Angle%

Fantasy Baseball Dynasty Buys and Sells

Are we buying Hunter Brown as an ace? Is he a top-5 dynasty SP at this point? This year has shown his dominance by posting a 2.04 ERA and a 0.91 WHIP in 61 2/3 innings. This is not a new thing, either. Dating back to last May, Brown owns a 2.22 ERA with 209 strikeouts in 194 1/3 innings.

Brown has shown improved command and is walking less than 7 percent of hitters. The strikeout rate has also jumped to nearly 31 percent thanks to a jump in stuff. Brown's 111 stuff+ is the fifth-best mark in baseball, while the 113 pitching+ ranks eighth, according to Eno Sarris' model.

When you have elite stuff and a six-pitch mix, you set yourself up for success. Brown has an elite 32 percent whiff rate on his four-seam fastball and has two other pitches with a 30 percent whiff rate. I think buying high on Brown is a good idea.

Geraldo Perdomo is a good sell-high in dynasty. Given that he is 25 years old and currently performing as a top 25 player, you have a good sell opportunity. In 225 plate appearances, Perdomo is slashing an impressive .302/.399/.473 with six home runs and 11 stolen bases.

So, why sell Perdomo? Perdomo has already reached a career high in homers and is pushing his career-best stolen base mark of 16. This is not to say that he is going to stop hitting homers or stealing bases, but regression seems likely.

While the exit velocities have improved, they are still well below average, and Perdomo's barrel rate of 4.8 percent ranks in the 18th percentile among MLB hitters. While I am not a huge proponent of expected stats, Perdomo's xSLG is .397, and the xBA is .262.

The contact skills are elite, but I expect Perdomo to continue trending toward career norms. If you can sell him for a top-100 dynasty asset, I absolutely would.

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