Article 16: Illegal Cut Block. See Rule 8, Section 4, Article 5. Section 3 Unsportsmanlike Conduct
Article 1: Prohibited Acts. There shall be no unsportsmanlike conduct. This applies to any act which is contrary to the generally understood principles of sportsmanship. Such acts specifically include, among others:
(a) Throwing a punch, or a forearm, or kicking at an opponent, even though no contact is made.
(b) Using abusive, threatening, or insulting language or gestures to opponents, teammates, officials, or representatives of the League.
© Using baiting or taunting acts or words that engender ill will between teams.
(d) Prolonged or excessive celebrations or demonstrations by an individual player. Players are prohibited from engaging in any celebrations or demonstrations while on the ground. A celebration or demonstration shall be deemed excessive or prolonged if a player continues to celebrate or demonstrate after a warning from an official.
(e) Two or more players engaging in prolonged, excessive, premeditated, or choreographed celebrations or demonstrations.
(f) Possession or use of foreign or extraneous object(s) that are not part of the uniform during the game on the field or the sideline, or using the ball as a prop.
(g) Unnecessary physical contact with a game official.
(h) Removal of his helmet by a player in the field of play during a celebration or demonstration, or during a confrontation with a game official or any other player.
Exceptions: It is not a foul if:
I. a timeout has been called for reasons of injury, television break, or charged team timeout; or
II. it is between periods.
Note 1: Under no condition is an official to allow a player to shove, push, or strike him in an offensive, disrespectful, or unsportsmanlike manner. Any such action must be reported to the Commissioner.
OFFICIAL NFL PLAYING RULES 70
From the NFL rule book. I believe section a. makes it pretty clear.