Oakland Raiders player Ray-Ray Armstrong is under police investigation for barking at a police dog and pounding his chest.
Armstrong, 24, reportedly lifted his shirt and taunted the animal shortly before the start of Sunday's NFL game against the Pittsburgh Steelers.
The linebacker could be charged with taunting a police K-9, a third degree felony in Pennsylvania.
"The dog was going crazy," chief deputy Kevin Kraus said.
"The deputy was trying to control the dog the best she could. We were immediately notified about the incident, and we immediately initiated a criminal investigation into the matter."
Police deputy Maria Watts, the dog's handler, identified Armstrong as the player involved in the alleged taunting.
She told WTAE Pittsburgh television that the player was shouting "Hey dog, hey dog" after leaving the locker room before the game.
"Bandit was very agitated. He wanted me to let him go. I imagine with his training and experience he would have gone to his target who was taunting him. I don't want to speculate on what he would have done," she said.
"No-one in the department, from the sheriff down, is happy about this."
A third-degree felony in Pennsylvania is punishable by up to seven years in jail and a maximum $15,000 (£9,900) fine. Other crimes in that category include 'reckless burning or exploding', 'terroristic threats' and 'carrying a gun in public without a permit'.
The local sheriff's office has notified both teams and the NFL that an investigation is under way.
The teams and the league declined to comment.
The Oakland Raiders were beaten 38-35 by the Steelers.