Scouting Report

Scouting grades: Fastball: 50 | Curveball: 60 | Slider: 50 | Control: 50 | Overall: 40

A Texas high school all-state performer, Peters began at Temple Junior College before transferring to Dallas Baptist University, where he earned second-team All-Conference USA honors. Primarily a reliever, he led the Patriots with four saves and made key spot starts, including a six-inning, 10-strikeout outing as part of a combined no-hitter against Liberty to close the regular season. Strong performances in Regional play helped propel him to Seattle’s fourth-round selection in 2025, when he signed for below slot value at $550,000.

At 5-foot-11, Peters is an athletic left-hander with the potential to develop into a starter. His fastball sits around 93 mph and can touch 96 mph, featuring natural ride that challenges hitters up in the zone. Behind it, he mixes an upper-70s curve that generated high whiff rates in 2025 and a low-80s sweepy slider, though the slider is used less consistently. Peters pairs his repertoire with a repeatable delivery and solid arm action, allowing him to command all his pitches and attack the strike zone effectively.

The next step for Peters as a starter will be refining a changeup and demonstrating he can handle a rotation workload, as he did not report to an affiliate after being drafted. Even if that path proves challenging, he projects as a high-floor left-handed reliever with three effective pitches. Paired with other top picks like Griffin Hugus and Kade Anderson, Peters represents another promising pitching piece in Seattle’s 2025 Draft class, offering both present value and long-term upside out of the bullpen or potentially in a rotation.

Scouting grades: Fastball: 50 | Curveball: 60 | Slider: 50 | Control: 50 | Overall: 40

An all-state performer during his Texas high school days, Peters began his college career at Temple Junior College. After two years there, he moved on to Dallas Baptist University where he earned second-team all-Conference USA honors. Pitching mostly in relief, he led the Patriots with four saves. He also made four starts down the stretch, highlighted by a 10-strikeout six-inning performance as part of a combined no-hitter against Liberty on the final day of the regular season. He pitched well in Regional action before the Mariners took him in the fourth round of the 2025 Draft and signed him for a below-slot $550,000 bonus.

While Peters doesn't have a huge track record, the Mariners think the 5-foot-11 athletic left-hander might have the chance to start. His repertoire begins with a solid four-seamer with good ride up in the zone that sits around 93 mph and has been up to 96. He has two distinct and effective breaking pitches behind the heater. His upper-70s curve elicited a 44 percent miss rate in college in 2025, per Synergy, and he differentiates it from his sweepy low-80s slider, which he doesn't throw as often or as consistently.

With a solid and repeatable delivery and arm stroke, Peters has shown he is capable of finding the strike zone with all of his pitches. In order for him to start, he's going to have to find a changeup that works and show he can handle a rotation workload. Worst case, he has a pretty high floor as an effective lefty reliever with three useful pitches.

Transactions

Team	Date	Transaction
	03/05/2026	LHP Mason Peters assigned to Seattle Mariners Prospects.
	08/04/2025	LHP Mason Peters assigned to ACL Mariners.
	07/19/2025	Seattle Mariners signed LHP Mason Peters.
	07/02/2025	Chatham Anglers released LHP Mason Peters.
	06/14/2025	Chatham Anglers activated LHP Mason Peters.
	06/14/2025	Chatham Anglers activated LHP Mason Peters.
	01/23/2025	LHP Mason Peters assigned to Dallas Baptist Patriots.