Seattle Mariners pitcher Hector Santiago was ejected from Sunday’s game against the Chicago White Sox after umpires checked his glove and discovered a sticky substance on the inside. This is the first ejection since Major League Baseball began cracking down on pitchers’ use of foreign substances. 

The 33-year-old left-handed pitcher was replaced midway through the fifth inning after umpires checked his glove — a requirement under the new league rule.

The glove was also secured by the umpires before being given to an MLB authenticator for further examination. The Mariners said they believe the examination will clear Santiago, who is facing a potential 10-game suspension. The Mariners would not be allowed to replace him on the roster while he serves the suspension. 

Crew chief Tom Hallion said the substance was “very noticeable” and that all of the umpires had agreed on the decision.

Santiago insisted the substance found inside his glove was legal. “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.” 

Mariners manager Scott Servais said the stickiness was likely due to a reaction between the rosin and sweat due to the heat and humidity during plat. “They’re following the rule,” he said. “They can go ahead and look at it. There’s no sticky stuff in the glove.”

MLB allows for pitchers to use rosin to help them grip the ball. Mixing rosin with other substances, such as sunscreen — previously a common additive for pitchers — is against the rules.

Santiago is currently in his first season with the Mariners. He has previously played with the White Sox, Los Angeles Angels, Minnesota Twins and New York Mets.