Roughing the holder in football is a penalty in which a defense player makes contact with the holder on a kick. The infraction results in a 15-yard penalty and an automatic first down being granted to the offense.
The holder is responsible for catching the snap and holding the ball in place for the kicker on a field goal attempt. The holder is often in a kneeling position and awaiting a signal from the kicker that indicates when he is ready for the ball to be hiked. This leaves the holder rather defenseless, which is why the rules explicitly state that any contact with the holder results in a penalty. Incidental contact is included in the ruling, with the only exception being if the defender is pushed into the holder by a member of the kicking team.
Roughing the holder can be an extremely costly penalty for the defense because it allows the offense to move up 15 yards and obtain an automatic first down. The offense is then inclined to take the kicking team off the field and send out the regular offense, increasing their chances of scoring a touchdown (worth 6 points) as opposed to the maximum of 3 points that could've been earned via the field goal attempt.