The way the sim does fouls, to my understanding, is as follows:
There are five players on the floor. Their foul rates are 1,1,1,3,1, four low foul players and one average.
The sim determines a foul. The player with the rate of 3 will be charged with the foul 42.9% of the time (3 of 7).
This is the same way that the sim determines who shoots, rebounds, etc, etc.