From what I remember is that the home team gets to chose which system can be deployed.
System A: Ball hand out to ball boys around the pitch and should a ball go in the ground or away somewhere then another ball will just be used.
System B: Only one ball is used, if it goes out of play in the ground somewhere then they have to wait until it comes back and the same ball will be used. It will only be replaced if it is broken.
you really do know the most random shit.