In a wooden floor built up to modern building codes a 750 kg hero is unlikely to break the beams, but he may cause some damage.
There are two problems with loads on floors and other structures: overall resistance of the floor and punctual resistance. That is, in a wooden flooring, that the beams don't break (making the whole flooring fall down) and that the plank where the hero is resting his foot don't break.
Since most (all?) building codes all over the world have rules to check for those two problems, I am going to take my numbers from the Spanish one (point 3.1.1, page 9) which must be quite similar to the numbers anywhere else. I'm using here kg/m2 although the code is in kN/m2 (1 kN/m2 = 100 kg/m2) for ease of comparison with a 750 kg hero.
Overall strength of floor and beams isn't going to be a big problem because floors are checked for an uniform load ranging from 200 kg/m2 for dwellings and hotel rooms to 500 kg/m2 for supermarkets. If the room isn't full, a 750 kg load is equivalent of the design load of a few square meters. Therefore, a 750 kg hero is only going to be a problem if the room is already full, or if at least the part of the room over the same beam where the hero is, is already loaded. For example, the hero should avoid attending a party in an hotel suit already packed with people.
The point load may be more tricky because structures are checked against loads of 200 to 700 kg on a 5 cm x 5 cm square. Then, in a wooden flooring, his weight might exceed the design load of individual planks. The best advice here would be to walk carefully trying to rest his feet only over the beams. That piece of advice could be hard to follow during a fight, but planks falling and the hero clinging to the beams might make great shoots for an action movie.
In addition to that, there is a relieving fact: strength is not the only condition that leads structure design, and very often the most stringent rule is against excessive bending. Therefore, very often beams can hold several times the design load without breaking, in spite of a large deflection that could be aesthetically unpleasant (or even frightening) and may cause cracks on non structural elements.
And a last cave-at: the OP says that the hero is fighting someone. If "someone" is a team of 750 kg villains or heavier, the situation may be trickier but using villains for load testing could be advisable and could lead to an interesting plot.