SEATTLE — Here lies the piggyback.

Even when it worked, it didn’t really work.

On paper, the Seattle Mariners’ piggyback pitching plan actually worked pretty well, with an unnatural tag team of Bryce Miller and Luis Castillo surrendering two combined runs in each of the experiment’s two outings. The starting pitchers were particularly potent, as Miller hurled 5 2/3 one-hit innings against the Chicago White Sox last week and Castillo added four scoreless frames in a 9-2 win over the Athletics on Monday. Scrape away the optics, and the piggyback has served its stated purpose, keeping Miller and Castillo stretched out while Seattle juggles six capable starters.

But it’s not worth doing that at the expense of everyone involved.

The optics, in this case, cannot be scraped away.

We all saw Miller, one of the most affable Mariners, shake his head and bound off the mound after being pulled last week. We all saw Mariners manager Dan Wilson mismanage the situation, when Castillo — in his first career regular-season relief appearance — was left in for the ninth inning, and a 1-0 lead devolved into a 2-1 loss. We all saw Castillo, a longtime clubhouse leader, spike his jacket and hat into the bench like a buried slider after receiving an early exit with a 7-0 lead Monday.

Another look at Luis Castillo after learning that his night was done.

Can’t recall ever seeing this kind of frustration in his nearly four years with the Mariners.

“For Luis Castillo to be as frustrated as he is, it’s because of the dirt under his spikes. He has earned every right, in my opinion, to be back out there, to get the lion’s share of this piggyback split here,” Dallas Braden, an MLB pitcher for five seasons, said on the A’s broadcast Monday. “And if he’s throwing the ball the way he has tonight, and if he has produced the way he has tonight, and you have the lead that you have tonight, help me understand why it’s not Luis Castillo back out on the mound right now.”

It’s actually not a difficult concept to understand. Though the Mariners have six competent MLB starters, they’d prefer to avoid a six-man rotation that would eat into starts for Bryan Woo, George Kirby, Logan Gilbert and Emerson Hancock. And considering Hancock’s emergence, Miller’s supercharged stuff and Castillo’s standing (and contract) with the club, there’s no easy boot to the bullpen. So, the piggyback allows Miller and Castillo bulk innings while delaying a more permanent decision. It also requires compromise and avoids commitment.

On paper, the piggyback checks boxes.

But here’s the problem. Paper doesn’t account for established roles, egos or personal pride. It doesn’t account for the repeatable routines and preparation pitchers rely on. It doesn’t account for confidence, which must be maintained in a six-month marathon. It doesn’t account for anything besides the bottom line. It’s a scientific solution to a human problem, which is why this experiment is unsustainable. With more than 100 games still on the schedule, the Mariners can’t afford to curdle clubhouse chemistry. They also can’t afford to keep giving away games.

The piggyback’s got to go.

Whether they turn to a six-man rotation or transition Castillo to a long-relief role, it’s time for the Mariners to pick a path. It’s time for commitment, communication and clarity, all of which have been lacking the past two weeks.

Given that Seattle’s starters own baseball’s seventh-best WHIP (1.17), and Castillo has been by far that rotation’s weak link (5.90 ERA, 1.510 WHIP, -1.0 bWAR), it seems obvious the Mariners would be better off with Castillo in the bullpen.

Of course, it’s risky to rankle “The Rock,” who’s due $24.15 million both in 2026 and 2027. Castillo’s contract also includes a $25 million vesting option in 2028, contingent on him reaching 180 innings the previous season. So, the 33-year-old three-time All-Star has ample motivation to remain in the rotation.

It’s also unclear how Castillo would perform in a relief role, considering he’s started 253 of 254 career regular-season games. But a beleaguered bullpen that has already absorbed injuries to Matt Brash, Gabe Speier and Carlos Vargas could obviously benefit from another established arm. And given the inevitability of injuries in baseball, Castillo could be back in the rotation sooner than later.

There isn’t an option that would suit all six starters. Relegating Castillo to relief would warrant a difficult conversation. But it would be a way forward — a plan, not a placeholder. The Mariners owe it to Miller and Castillo to provide clear communication and distinct, defined roles. Miller said he wasn’t informed he’d pitch out of the bullpen until a day or two before Monday’s game, a disservice to the 27-year-old should-be starter.

When asked on the Mariners.TV broadcast Monday if he’s becoming more comfortable with the piggyback, Miller said after a prolonged pause: “This setup’s not very comfortable. But like I said, at the end of the day I get to come out and pitch in the big leagues, something I’ve dreamed about my whole life. Would I rather start the game? Yeah, but any time I can be on the mound in the big leagues I’ll be grateful for it.”

I’m guessing he didn’t dream of entering in the fifth inning of a science experiment at a minor-league park in Sacramento.

The piggyback was a placeholder, and now it’s got to go.

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