The harness is worn directly over the skin, and if you paid attention to how to "score" the first point in the helmet's post, it should be obvious how one "scores" the winning point.

A contestant is going to do everything they can to prevent being "scored on" but the protective gear might make it difficult to hang on since the gloves are padded, MMA style, to prevent against broken hands. The goal is to subdue and pin an opponent, not knock them out; the audience doesn't find points scored against unconscious constants all that interesting.

Some less sportsmanlike contestants have figured out how to tangle a gladiator in their own gear, giving them a much easier time against a squirming and screaming opponent whose helpless protestations are far more desired by the crowd watching live and the those with private scrying devices at home or at a drinking establishment that also give the viewers closeups and running commentary (it's a world with magic, I don't gotta explain shit lol).