LOS ANGELES — Running back Anthony Brown has quit USC’s football team, and coach Steve Sarkisian was stunned Thursday by Brown’s apparent accusations of racism against him on social media.

A photo of the words “Couldn’t play for a racist man!!!!” was posted on what USC said was Brown’s Instagram account. The posting was later deleted.

“Sark treated me like a slave in his Office,” was posted in the caption to the photo, along with the hashtag “Fighton.”

Sarkisian was told about the apparent posts from Brown, who is black, shortly after USC finished practice Thursday. The visibly disturbed coach called them “ridiculous,” saying Brown had shown no indication he felt slighted or insulted in their relationship.

“If you ask anybody in our building, any of our players … that’s about the furthest thing from the truth,” Sarkisian said. “Quite honestly, I’m shocked.”

Brown’s acrimonious departure is another blow to a program already reeling from the bizarre saga of cornerback Josh Shaw, who was caught in a lie about the circumstances in which he sprained both of his ankles last weekend. Shaw has been suspended indefinitely.

Brown is a senior who played cornerback for the Trojans until this season, starting two games in each of his first three seasons. He played in only two games last season because of ankle injuries, racking up nine tackles at Notre Dame before missing the final eight games.

He switched positions to running back for his senior year, but Brown missed most of training camp with a hyperextended elbow.

“I had encouraged him to play,” Sarkisian said. “I wanted him to play. I didn’t want him to quit, and I thought he could get healthy.”

Sarkisian said Brown asked the coaches to allow him to play running back this season, and the staff agreed with his move to a talent-rich position at Tailback U. After missing most of camp, he is listed sixth on USC’s depth chart behind returning starters Javorius Allen and Tre Madden, as well as talented backups including Justin Davis.

“We thought he could be an asset to our team, especially when healthy,” Sarkisian said. “(USC) really tried to make it a point to accommodate the position change. He wanted to move to running back. We did so. He unfortunately got injured and was working his way back in training camp, and decided he didn’t want to play anymore.”

Several current Trojans and Heisman Trophy-winning quarterback Matt Leinart immediately jumped on social media to defend Sarkisian. The first-year USC coach and former Trojans assistant hasn’t even appeared on the Coliseum sideline this season before dealing with another dose of the turmoil that seems to follow this vaunted program.

“Coach Sark is who we all believe him to be,” USC receiver George Farmer posted on his Twitter account. “Accusations like those couldn’t be more untrue.”