Dear @sam12,
Great question. I’m an Australian, so when I think of football I think of this:
Even in this sport (which I think we can say is a bit more contact-based compared to soccer and so holds more potential for blood-to-blood exchange), there is no detectable increased risk of transmission (https://onlinelibrary.wiley.com/doi/abs/10.5694/j.1326-5377.1995.tb139908.x). Indeed, there is what’s called the blood rule in AFL, which means you do get sent off if you have a bleeding wound, which does help control for transmission.
Hope this helps,
Thomas