Just the one (if you're talking proper football, the one where you use your feet...)
every football game only needs only one refree in it.
1 referee, 1 4th official, 2 line officials, 2 goal line referees. In total there are 6 officials in most games.
22players + 1refree and 2assistance refree
There are seven officials on the field during a football game.
There are 90 minutes to a football game, plus injury time to be added.
11
one
42
5400
Seven
1 foot is required. 2 is required only in professional
17 players are required according Football Sequence 49.381
36
I don't think that it is required but i believe many football players do ballet because it is a good way to become more flexible. Being flexible can help out with their football.