Give referees a set of Ratings that determine their odds of making a certain decision. For example, one could be like this -
Foul - 65
Yellow Card - 70
Red Card - 35
Penalty - 90
Tolerance - 60
This ref calls a pretty tight game, not shy with the yellow cards, and doesn't hesitate to award a penalty. The tolerance rating determines how many fouls one team or player is allowed to get away with until a card has to be given. Once the referee's tolerance is full the CPU or human opponents need to be more careful when defending. Both teams need to know this though.
Foul - 65
Yellow Card - 70
Red Card - 35
Penalty - 90
Tolerance - 60
This ref calls a pretty tight game, not shy with the yellow cards, and doesn't hesitate to award a penalty. The tolerance rating determines how many fouls one team or player is allowed to get away with until a card has to be given. Once the referee's tolerance is full the CPU or human opponents need to be more careful when defending. Both teams need to know this though.