This phrase is used in football to describe a play in which a player on the defense attempts to block a punt or field-goal and makes contact with the kicker. Depending on when contact was made and the severity of the contact, it may, and often does, result in a penalty. Punters and field-goal kickers are protected with rules because while kicking the ball their legs are very susceptible to injury if they are hit or tackled. In cases of incidental contact, or if the kick is blocked and then contact is made, there is usually no penalty.
Prior to the rule which protected kickers, they would get injured when a defensive lineman or other large player would make contact with their leg while in motion. Since kickers typically wear little to no padding on their legs, this could result in season or career ending injuries. The original rules were put in place in 2005 and expanded in 2010 to include special provisions for kickers on kick-offs.