Back when the Ultimate Fighting Championship (UFC) was in its infancy, there were very few rules. Ex-presidential candidate John McCain actually described it as the human equivalent of a cock fight, and to be fair to him, the lack of rules made for a rather unsavoury spectacle in some cases.

One of the most notable cases in question happened in UFC 4, when strikes to the groin were completely legal. It saw Keith Hackney punch Joe Son (in the photo) square in the groin repeatedly, and Keith unsurprisingly went on to win the fight.

It was cringeworthy, but it also spawns an interesting ‘prisoner’s dilemma problem’ (see one of my previous articles for a more in-depth description)

The payoff matrix below could be one possible representation of the problem:

I’ve chosen values for each of the outcomes as follows:

  • If neither fighter gets hit in the groin, it’s status quo. Nobody benefits and nobody suffers.
  • If both fighters hit each other in the groin, they both suffer, but arguably not as badly as when only one gets hit – the benefit of having your opponent in pain offsets the loss somewhat.
  • If one fighter hits and the other doesn’t, then there’s obviously a huge advantage for the aggressor.

In reality, there are a couple of points to be made. Firstly, the game could be seen as being repeated, but then the payoffs would change each time.

Secondly, the argument could be made that the person who hits first has such an advantage that the other person would not be able to groin strike back. In this case, the game would turn into a sequential game rather than the simultaneous game I have assumed above.

What are the outcomes?

The Nash Equilibrium is found when both fighters hit each other in the groin, because in this game, the ‘hit groin’ action completely dominates the ‘don’t hit groin’ action for each player. If you wanted to stand the best chance of winning the fight, it would have made sense for you to come flying out of the blocks and go for the groin.

Funnily enough, in most fights in the UFC when groin strikes were permitted, most fighters chose to make some form of implicit ‘gentlemanly’ collusive agreement, where neither hit each other in the groin out of principle. This seems to be an unwritten rule for male fights in general, and is respectable.

However, it’s not the rational choice! The reward if one fighter breaks the unwritten agreement and decides to hit the other in the groin is so great that it doesn’t make logical sense for him not to! Keith Hackney was unloved, but possibly one of the more rational fighters in the UFC at the time.

I think this is one of the situations where I’m glad that people are not entirely rational all the time!