The risk is definitely small, probably not quantifiable, but also not zero.
The risk of HIV transmission would also fall for players on treatment (extrapolating from other groups). Hepatitis B and C are actually more transmissible but the majority of afl players would be low risk for these two being generally born in Australia and not injecting drug users.
I would say the risk of catching a BBV playing footy is almost certainly less than something worse happening to you like a severe spinal injury. But the difference is however small, this risk can be reduced by removing the player briefly, so even though the NNI (number needed to interchange) would be very very high, it’s probably worth doing.