I tried looking for an answer, but couldn't really find anything so figured I'd ask here. My current sim is maxed with the martial arts skill, as well as the athletics skill, yet when I spar I seem to lose more often than I'd like to people with lower skills. I know in real life someone with less skill could potentially get lucky, but this is a video game and I just hate that my sim is losing to anyone that has a lower skill. So what exactly affects if you win or lose when sparring? I read somewhere that success is based on how much time you spend sparring, is that true?

The sparring is bugged, so I'm pretty sure it's completely random. It was supposed to take your martial arts skill into account, but it doesn't.

Well that explains it. I guess the only real point to having a high skill is to be able to meditate, train other people, and to have fancier moves when you spar. It definitely seems random, because last time I tried to spar my opponent had half my skill (10 compared to 5) and they beat me 2-1, then I won 2-1, then lost again 2-0. Does that perk for doing 75 sparring matches help at all? If sparring is bugged I'm just wondering if that would even have any affect, and if it's worth doing 75 matches to get.

It appeared to have an effect, but I haven't poked into the code to be certain.

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Actually, no. The skill does count. You're referring to fighting. When Sims fight, Martial Arts skill is supposed to contribute their chance of winning, but it's bugged and doesn't work as intended. Higher Athletic skill increases the chance of winning a fight, but Martial Arts skill is bugged. If only one of the fighting Sim has a Martial Arts skill of any level, they will win regardless of any other factors. If neither or both of the Sims have Martial Arts skill, the skill is ignored and basic calculation to determine who will win applies.

The way that a sparring match winner is determined is as following. A Sim gets +10 points for each Martial Arts skill they have and +5 for each Athletic skill. If they have "Meditative Focus," "Oddly Powerful," or "Pumped" moodlet, or Disciplined trait, they will get additional +5 points each. If the Sim has completed Sim Fu King challenge, they will get +25 points. Both the Sim and their opponent will have their own points based on that. If Sim A has 50 points and Sim B has 30 points, the chance Sim A will win is 50/80, while Sim B is 30/80. The winner is determined if they have won 2 rounds in a match.