[Allison K]

I think it mostly has to do with the venue size. In Pittsburg we were allowed to have 8 people around the field, but in Detroit (Read: really small venue) we could only have 5. Both regionals we were allowed to swap out team members, so it didn't have to be the same 8 or 5 the whole time, just no more than 8 or 5 at once. Also at both regionals the extras could be adults or students.