"Cavanaugh is being treated for rabies as a precaution—experts say beaver attacks on humans are rare, and most are either a result of rabies or a beaver trying to protect its offspring"
It's a possibility that the beaver had rabies. The treatment is very painful, but it's preferable to death.
I've never heard of a beaver starting a fight.
Rabies should be assumed until you can rule it out, imo. Despite the advances claimed for coma therapy- it's still assumed to be 100% fatal. The girl who was successfully treated had actually received preliminary treatment before her infection developed fully, so many attribute that to her survival. Treatment is less painful now than before.
Incidence of infection in animals seems to be on the increase--it seems to be cyclic, almost a sine curve when charted graphically.
Stories like this are good reminders: once the disease fully develops, you die and in unspeakable agony.