[JugglingReferee]

Many people bite their lip to prevent themselves from saying something.

Maybe this player bits his shirt. By biting his shirt, he could be preventing himself from verbalizing a profanity. Maybe it's his own preventative playing. I like to penalize the more obvious situations, such as profanity, punching the matts on a wall, hand gestures, or throwing a mouthguard at me.

Edit: Knowing now that the player cursed at the official, the T was the proper course of action. Once a player swears, the shirt biting is not meant to show up the official. It's just personal frustration by then.