Unnecessary roughness is a penalty in football that is called when rough contact, deemed unnecessary, is made against a player who is often ruled defenseless. When an offensive player commits this penalty, it results in a 15 yard loss and a replay of the down for the offense. When a defensive player commits this penalty, it results in a 15 yard loss for the defense and an automatic 1st down for the offense.
There are certain criteria for what defines a defenseless player in the NFL rulebook, such as a player who just threw a pass, a player who is coming to the ground after missing a catch, or a player who recently ran out of bounds. If rough contact is made against any defenseless player and the contact is ruled unnecessary by the officials, unnecessary roughness is called against the offending player.
A facemask penalty or clipping penalties are also considered unnecessary roughness but they are dangerous enough penalties to enforce a personal foul rather than a regular penalty.