Emotions boiled over and got the best of Panthers quarterback Cam Newton at practice yesterday, culminating in a heated scuffle.

Fights are common in training camps but rarely involve franchise quarterbacks. Newton went at it with cornerback Josh Norman, a skirmish that ended with both players at the bottom of a pile and having to be separated by teammates. Neither player was injured.

The altercation occurred after Norman made a sliding interception of a pass thrown by Newton, got up and began to return the ball toward the opposing end zone, as defensive players are instructed to do by their coaches. Newton pursued him, and coach Ron Rivera said Newton got stiff-armed by Norman along the way.

As the whistles blew, signaling the end of the play, Newton sped up his pursuit of Norman and tackled him near the end zone. The two wrestled on the ground for a few moments as some other players piled on.

Newton and Norman eventually were separated. An irate Newton got up shouting at Norman -- "Hit me like that again and you'll know something!" -- as he was being restrained.

Rivera said this usually is the time during training camp when tempers began to flare but added, "You really don't expect it to be your quarterback."

Rivera, who played nine seasons for the Bears, was asked if he had ever seen a quarterback go after another player in practice. He joked, "Yes. Remember, I played with Jim McMahon."

WR Smith: '15 my last year

Ravens receiver Steve Smith, 36, said he will retire at the end of the season, his 15th in the NFL. He announced that he will walk away after the second year of a three-year deal with Baltimore. "I feel like it's time," he said. "My body feels great, but not everybody gets this opportunity."

Smith is one of 12 players in league history to record 900 catches, 13,000 receiving yards and 70 touchdown receptions.

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Patriots release QB Flynn

Still unsure of the status of Tom Brady and with the preseason opener coming up, the Patriots released quarterback Matt Flynn and signed Ryan Lindley to replace him as the team's third-stringer. Flynn signed with the Patriots on June 12 but was on the non-football injury list. He previously played with Green Bay, Seattle, Oakland and Buffalo.

Lindley was forced into a starting role for Arizona late last season and struggled.

Browns' Thomas injured

The Browns are awaiting further test results on Pro Bowl left tackle Joe Thomas, who injured his right leg in practice. Thomas has never missed a play in his NFL career, which began in 2007. -- AP