Bruce Arians Fined $50k For Slapping Player's Helmet During Game

Bruce Arians will have to pay up for slapping his own player's helmet during last weekend's playoff game ... 'cause the NFL is fining him $50k for the incident.

The moment happened during the Bucs vs. Eagles Wild Card game on Sunday ... after Philly receiver Jalen Reagor fumbled a punt return and Tampa Bay recovered.

During the pileup, Bucs safety Andrew Adams appeared to try to get Philly players out of the way ... which pissed Arians off to the point of striking the 29-year-old in the helmet.

The whole thing was caught on camera during the broadcast ... with Troy Aikman admitting he was puzzled by Arians' actions.

"He takes a wack at Adams," Troy Aikman said at the time. "Not exactly sure what that's about."

The 69-year-old coach explained after the game that he struck Adams to avoid a penalty.

"You can’t pull guys out of a pile," Arians said during postgame interviews.

"We just got a big play, great field position, and he’s trying to pull a guy out of a pile, and I was trying to knock him off of that guy so he didn’t get a penalty."