SEATTLE — During the seventh inning Monday night at T-Mobile Park, the Seattle Mariners and Oakland A’s experienced a significant delay in their series opener.

When Mariners right-handed reliever Cory Gearrin was called in from the bullpen to relieve starter Yusei Kikuchi, umpires approached Gearrin on the mound as he completed his warm-up pitches.

Confusion on the field followed as umpires spoke with Gearrin, and Mariners manager Scott Servais left the dugout in search of an explanation. He was told a toe-tap motion in Gearrin’s delivery was violating a rule.

The lengthy delay continued as umpires contacted officials New York to get an official ruling, and it was decided Gearrin’s motion was illegal.

“Cory does a little thing with a toe tap,” Servais said following the game. “He lifts his leg, puts his toe down, and then goes again. It was brought to my attention today that that is an illegal pitch.”

Should Gearrin have thrown a pitch after a toe tap, it would be considered a ball. If a runner was on base at the time of the pitch, it would be considered a balk, and the runner would advance.

Gearrin said he has thrown with this delivery for multiple seasons and has never been approached by an umpire about it.

“I did it last year when I was with Texas. I did it with Oakland. I’ve done it all this year,” Gearrin said. “Tonight was the first night I’ve heard anything about it. It’s just one of those things. The game is weird. I’ve never come in and had to wait on a ruling.

“Whatever they say is kind of what you have to deal with, so you make an adjustment and keep going.”

Servais, a former MLB catcher, said he had never seen a pitcher approached about that particular motion being illegal either. He discussed the ruling with the umpires for several moments, and was not allowed to cross the first-base line to talk to Gearrin without being charged with a mound visit.

“You cannot touch your foot twice,” Servais said ahead of Tuesday night’s game. “I’ve never seen it enforced like that. … Over the years I’ve seen a lot of guys do it and never have an issue with it.”

Gearrin (0-1, 3.63 ERA) was able to make a quick adjustment, and tossed a scoreless inning in the seventh, allowing two hits and striking out two.

“It was different,” Gearrin said. “It’s basically changing your delivery. But, I just tried to make it as comparable as possible. I still was trying to lift and come as close to the ground as I could to stay over the rubber and still have the same rhythm, just without touching.”

“It’s pretty hard when you’re used to doing something as a pitcher and they change you mechanically,” Mariners catcher Omar Narvaez said. “He handled it pretty good.”

Servais assumed the umpires were likely tipped off about Gearrin’s toe tap, though there was no indication of who signaled the umpires to look for it.

Servais said he’s seen other pitchers, such as former MLB reliever Robb Nen, throw with a toe tap in their delivery in the past, and questioned why it was brought up now.

“He did it his whole career, and that’s exactly the argument I gave the umpires last night,” Servais said. “I caught Robb Nen in the late 90s, and I said Rob Nen pitched in this league for like 12 years. Nobody said a word to him.”

Servais said he has also seen other current pitchers use a similar approach to Gearrin’s — just without touching the ground.

“His delivery, kind of his whole tempo, is unique,” Servais said. “It is a slower pace. But, the toe tap is kind of a big thing just because it’s kind of his reminder to stay back over the rubber. You’ll see some other guys who will do a similar type thing, they just don’t quite touch the ground.

“Kenley Jansen, (Clayton) Kershaw, they all kind of do a similar type thing, but Cory was actually just touching the ground. That’s illegal to do, so he now knows that and he’ll make adjustments.”

Gearrin has allowed just two runs in his past 14 appearances, completing 13 innings with a 1.29 ERA during that span.

“I’ll just keep trying to feel it out and make adjustments,” Gearrin said. “I definitely don’t want to give any free pitches or free bases.”