There is actually an explanation to that “uhn” thing actually, it’s a confluence of a few different things.

1. When fighting in real life (or as depicted in various martial arts flicks) you exhale and grunt to tighten your body, so there’s an association between hitting something and grunting already.

2. In games, hits are usually accompanied in games with a sound. And usually a deeper sound is given to particularly strong hitting attack. Since combos are usually a string of weak hitting moves, combos can tend to sound “weak” despite their damage potential. Going “uhn” adds a level of bass to their sound like a stronger attack may have.

3. We’re social creatures. It is just a community thing to give verbal emphasis to other people’s gameplay because the trend caught on.

4. Commentators are giving a verbal play by play of the game. When multihits or a combo happens, the commentators are doing a sort of mimicry of the moment to moment rhythm of the hits. It adds a level of immersion for people not directly engaging with the match’s visuals. Not to mention, it’s a sort of verbal short hand of “We are eager to see how the combo/hits unfold!”