What became Jon Gruden's famous trademark?

Jon Gruden’s famous trademark became his scowl.

Gruden’s intense facial expression was a recurring feature of his public image as an NFL coach and television analyst. During games, broadcasts frequently showed him grimacing, glaring or contorting his face while reacting to players, officials and dramatic moments on the sideline.

The expression became especially associated with Gruden during his coaching years with the Oakland Raiders and Tampa Bay Buccaneers. He later became widely known to a national audience through Monday Night Football, where his animated reactions and forceful commentary reinforced the image.

His scowl is sometimes confused with his nickname, “Chucky.” That nickname referred to his resemblance to the horror-film character and was helped by his facial expressions, but it is not the same answer. Gruden’s raspy voice, aggressive coaching style and catchphrases were also recognizable traits; the trivia clue specifically points to the scowl.