Three Seattle Mariners’ Prospects That Have Disappointed This Year

#3: Mariners A-Ball RHP Juan Then – 5 GS, 7.11 K/9, 3.79 BB/9, 4.26 ERA, 4.87 FIP

Then really hasn’t struggled all that much this season, he makes the list largely due to his prospect ranking and the fact that there aren’t a lot of Mariner prospects who have struggled. Fangraphs currently has Then as the No. 11 prospect on their list, and MLB.Com has him as the Mariners No. 8 prospect in the system.

Then’s early struggles aren’t terribly surprising considering he is only 21 and has only thrown 65 innings above Rookie ball. The walks will likely come down with experience, but the low strikeout numbers are a little concerning, especially considering Then sits in the high 90’s with his heater.

What could ultimately be in store for Then, is a move to the bullpen. The heat is there, but he may not have enough of an arsenal to make it as a starter. And it has to be considered that the Mariners have a lot of potential starting pitchers in the system. Logan Gilbert already looks like an MLB pitcher, and both Hancock and George Kirby have been dominant as prospects. It’s not totally out of the question for Then to take the Edwin Diaz route and eventually move to the bullpen.

If Then can continue to develop the fastball and slider combo and add a more consistent change-up, then he should be fine. But as of right now, Then’s 2021 campaign in Everett has been a tad underwhelming.

#2: Mariners A-Ball 3B Tyler Keenan – .163/.315/.349, 1 HR, 14.8 BB %, 38.9 K %, .316 wOBA, 94 wrC+

Keenan’s first two months as a professional baseball player have not gone swimmingly for a multitude of reasons. He’s been on the IL since May 28, and before that, the bat wasn’t there for Keenan. When the Mariners took him in the 4th round of the 2020 MLB Draft, the expectation was they were getting an advanced bat with big raw power. Keenan was one of the hottest hitters in the nation at Ole Miss before COVID canceled the 2020 season.

But so far, the bat hasn’t translated to the professional level. The strikeout numbers are problematic, as is the lone home run in 43 at-bats. And for Tyler Keenan, the bat is the selling point. He doesn’t have plus speed and is only an average defender at best. Long term, he’ll probably end up at 1st base anyway.

The good news for Keenan is that this is a small sample size and it’s his first professional season. It’s only been 12 games, and his line drive percentage is at 31.8 percent which suggests some better luck may be heading his way. And the OBP is respectable despite the lack of hits. There is of course a long way to go in Keenan’s progress, but the first dive into pro ball hasn’t gone well for him.

#1: Mariners Low A-Ball RHP Damon Casetta-Stubbs – 6 GS, 11.52 K/9, 6.12 BB/9, 6.84 ERA, 6.39 FIP

It has been a bit of a nightmare 2021 campaign for the 21-year-old Casetta-Stubbs. The 11th round pick of the Mariners in 2018, the organization was hoping to get an arm with big-time upside and raw talent that could develop down the road.

But that hasn’t happened. Casetta-Stubbs is now in his third year with the organization, and control issues are still lingering in a big way. The BB/9 rate is way too high for a near 22-year-old arm still pitching in Single-A. The strikeout numbers are good and have been good throughout his career, but it’s not enough to counter the walk issues.

The one silver lining for Casetta-Stubbs is that he isn’t getting hit all that much. Opponents are only hitting .219 against him, which does offer hope that if he can limit the walks, he can still be effective. The issue is, there isn’t much to suggest that will be the case. It’s been his biggest problem since making his pro debut, and unless something changes in a big way, it’s hard to see him making it much further in the organization.

Like with Then, it is possible the organization tries to move Casetta-Stubbs to the bullpen but it would like a last-ditch effort to try and find something that works for him.