The official referee of the game will have an "R" somewhere on their uniform that stands for "referee." A uniform with the letter "U" stands for "umpire," the letter "H" or "HL" stands for "head linesman," "L" or "LJ" stands for "line judge" and "S" or "SJ" stands for "side judge."
In most college football conferences, it is required that several referees be able to help dictate the official rules of the game. The referees are there to help decide what fair calls are and to decide whether a move was illegal or not. Since football is played over a large area, more than one referee is necessary. The main referee, or the person who wears the "R," is the ultimate deciding factor and can go against what the other referees on the field say. The referee usually does not do this, but instead relies on the guidance of the other referees to understand how a play happened. The umpire is the next step down from the referee and presides over all of the line plays. The umpire is in charge of calls that are made by the head linesman, side judges and line judges. These judges are constantly watching their own area of the field and will be able to make the call as to whether a play was illegal or not.