The NFL penalized Jacobs for making obscene gestures and yelling obscenities toward fans in the stands at Philadelphia's Lincoln Financial Field before his team's 27-17 loss to the Eagles on Sunday.
In a letter to Jacobs, NFL executive vice president of football operations Ray Anderson described the conduct as "unprofessional and unbecoming as an NFL player."
Anderson added: "Repeated violations will result in increased disciplinary action, which may include suspension for conduct detrimental to the league." It was the second violation by Jacobs this season. He was fined $10,000 for tossing his helmet into the crowd during a Sept. 19 game between the Giants and Indianapolis Colts.
Jacobs apologized for that incident on the team's website, saying he had tried to throw his helmet on the sidelines but it had accidentally landed in the crowd.
