OK, lets say it's a grizzly bear and an equivalent sized shark. Something like a hammerhead. They're fighting on a beach. The bear is up to his thighs in water, so he can still fight and move properly.The water is deep enough to allow the shark to attack without fear of being beached, but not so deep that it has an advantage over the Bear. Both animals are healthy... Who you gonna bet on?
Why a shark? Would it not be more evenly matched if it was a Crocodile vs a Grizzly. Both have the advantage of moving fairly easily in both water and on land and both have the same weight.