A referee of a football game was killed and Mr. Numpad called his son RiddleLock to solve it. Here's the story: Mr. Referee was killed 3 hrs. after the american football game. He was found lying on the floor left hand is holding his right hands wrist, right hand closed. 5 players are being suspected, Mr. Kicker, Mr. Foul, Mr. Tackle, Mr. Touchdown, Mr. Strong and Mr. Cornerback.
RiddleLock Laughs and said that he knows the killer.

Who's Mr. Referee's Killer?