Mariners may have sealed slumping rookie's fate with shakeup at second base

What started as one of the more exciting storylines of the Mariners’ 2025 season now seems to be winding to a quiet conclusion. Rookie second baseman Cole Young, another symbol of Seattle’s youth movement and a beacon of upside at the keystone, appears to have lost his grip on the job. And the Mariners have made their most definitive move yet to signal that shift.

Young’s debut came with the usual rookie growing pains, a few defensive missteps here, some inconsistencies in production at the plate, but none of it felt disqualifying. Fans embraced the process because the potential was obvious. You could see it in the swing, the plate discipline, and the way he carried himself at just 22 years old. The Mariners weren’t just hoping Cole Young would become a franchise cornerstone, they were letting him prove it on the fly.

But potential doesn’t always line up with postseason urgency.

Mariners may have made up their minds on Cole Young

Right now, that urgency is trumping development. After going 2-for-38 in his most recent stretch, Young has been benched for five consecutive games, including Monday's opener of a three-game set against the St. Louis Cardinals. The Mariners have faced only two southpaws starting on the mound during that span, confirming this isn’t about matchups. It’s about production. Or more specifically, lack thereof.

Seattle has reached the point in the season where every inning matters. There’s simply no room for extended growing pains when you’re fighting tooth and nail in the AL Wild Card race. And so, with quiet decisiveness, the Mariners appeared to be reopening second base for Ryan Bliss.

At least they were, until Bliss suddenly had to stop his rehab from a torn biceps in its tracks and undergo surgery for a torn meniscus on Monday:

Second base was his job to begin the year, and he looked the part of a starter after beating out Dylan Moore for the role in spring training. The energy was high, the glove was steady, and he offered just enough offense to keep things moving.

With Bliss' season now officially over, Mariners fans must asume that a door that might have closed on Young is now still open. Yet if the team wanted to give him another chance, it surely would have done so by now.

What the Mariners seem to have determined instead is that Jorge Polanco and Leo Rivas is a workable platoon at the keystone. They have shared starts at second base over the last five games, which has allowed Dan Wilson to get Cal Raleigh out of the crouch with DH duty twice already.

The Mariners likely know better than to expect too much of the 32-year-old Polanco on defense at this stage of his career, but his bat is more than worthy of second base — especially lately, with his last 17 games resulting in a 1.163 OPS and seven home runs.

For his part, Rivas gives off utility infielder vibes that are simultaneously fair, yet potentially underselling him. He posted a .471 OBP in 66 games for Triple-A Tacoma, and has maintained an OBP north of .400 in 35 games at the big league level as well. He's an ideal candidate for the No. 9 hole on days when he starts.

As long as this tandem holds, the writing feels etched into the T-Mobile Park dirt: Cole Young is likely off the playoff roster.

It’s a tough pill to swallow, but shouldn’t be considered a failure by any means. If anything, this season offered the Mariners a glimpse of what’s to come. Young's future in Seattle remains incredibly bright, even if 2025 might not be his October.

In the big picture, this is a good problem to have. In Young and Bliss, the Mariners have two young infielders with real upside for 2026 and beyond. They’re not scrambling to find bodies, they’re deciding which of their talents gives them the best shot at extending the season.