NEW YORK (AP) - The NFL reminded teams of the rule prohibiting defensive players from mimicking the offense's signal-calling cadence after Dallas accused the Washington Redskins of causing the Cowboys to bungle several snaps.

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As part of a memo sent to clubs this week, the league reiterated that it was unsportsmanlike conduct for defenders to use "acts or words" that were "designed to disconcert an offensive team at the snap."

New Dallas center Phil Costa misfired on four snaps in Monday night's win, and afterward the Cowboys accused Washington of mimicking quarterback Tony Romo's cadence, which the Redskins denied.

"Due to the fact that the umpire is positioned in the offensive backfield for most scrimmage plays, no official is within close proximity of the line of scrimmage," the memo said. "Therefore it is more difficult to determine if a defensive player is imitating the quarterback's cadence and/or snap count.

"If it is determined by video review or other means available to the league office that defensive players are engaging in such practices, such players, and their position coaches, coordinators, and head coaches, will be subject to disciplinary action."