Seattle Mariners pitcher Hector Santiago has received a 10-game suspension for allegedly violating Major League Baseball’s foreign substance rules, the league announced Tuesday. Santiago is the first to be disciplined under new league protocols, which are designed to step up enforcement of rules meant to prevent pitchers from applying substances to the ball to improve their throws. 

The alleged violation occurred on Sunday, when Santiago was ejected from the Mariners’ game against the Chicago White Sox in the fifth inning after umpires checked his glove and found a sticky substance on the inside. 

Santiago’s glove was given to an MLB authenticator on Sunday night for further examination, according to CBS Sports. Crew chief Tom Hallion said the sticky substance was “very noticeable.” 

Santiago has denied putting anything other than rosin in his glove. Rosin is a permitted substance, but pitchers are not allowed to mix it with other additives, like sunscreen. 

“All I used was rosin,” he said. “I used it on both sides, trying to keep that sweat from dripping down to the hands. That’s the only thing — I used rosin, that’s about it.” 

Hector Santiago #57 of the Seattle Mariners pitches in the third inning against the Chicago White Sox at Guaranteed Rate Field on June 27, 2021 in Chicago, Illinois. 

Quinn Harris / Getty Images

Santiago’s suspension was slated to begin Tuesday night, when the Mariners face the Toronto Blue Jays. But the league said that because Santiago is appealing the decision, the punishment will be delayed until the appeal process is complete. 

The Mariners have backed Santiago, saying that they believe further examination of the glove will clear him.

MLB began increasing enforcement of its foreign substance rules on June 21. Umpires are now required to check pitchers, including their hats, gloves and belts, for any banned substances during games. Several pieces of equipment have been tossed before a half inning has gotten under way, but the inspection that led to the discovery of the substance on Santiago’s glove occurred after he had already pitched, forcing the umpires to eject him from the game.