He's probably talking about fights between wild animals (bear vs tiger etc.) or fights between spiders, scorpions, bugs.. not about illegal dog fights or anything like that, duh.
His question is legit.
Maybe you could create a site where people could have useless "which animal would win if animal X fought against animal Y" debates and polls. You could send people to your site by telling them they can find even more animal fighting videos there. You could use facts on animal fighting stats as content (about the insane strength of hyena jaws, for instance).
But it's not easy to monetize the whole thing properly 'cause you don't know in what type of products people looking for animal fights might be interested in.
Sell them dvds of old godzilla movies. Godzilla vs mothra. Some big animals in action, duh.
Naw, seriously, it's not easy to make a lot of cash with that type of traffic. But you could give your best and make the most out of it. I hope I could give you some ideas.