Crab-fights often involve a number of fighters on a "winner stays on" basis, with the winner of the first fight taking on a new challenger, and continuing until defeated, whereupon his vanquisher stays on to meet the next challenger.
Crab Fighting Rules
Each crab-man has three combat stats: Strength, Skill, and Speed. These are rated d12, d10 and d8 in whichever order is preferred. Each round, the players roll initiative - i.e. their Speed dice. The winner (highest number) gets to choose whether Strength or Skill is going to be crucial this round.
Then fighting begins. Here, each player rolls their relevant dice, for Strength or Skill. The highest one wins. If the loser has less than half of the total of the winner, he loses immediately - he is tossed onto his back. If he has half or more of the total of the winner, he is still in the round, but is in a weakened position. The winner now gets to roll an additional d6 together with his stat dice and add the totals for the next roll.
The players roll again. Once more, if the loser has less than half of the total of the winner, he loses immediately, and if he has half or more of the total of the winner, he stays in the round but the winner gets to roll an additional d6. Additional d6s are not cumulative - a winner does not get to roll 2d6 if he wins for two consecutive throws.
One the dice have been rolled three times, and there is still not a clear loser, a second round begins and initiative is rolled again, and the process is repeated.
Titchy is fighting Bull. Titchy has Speed d12, Skill d10, and Strength d8. Bull has Strength d12, Skill d10, and Speed d8.
Initiative is rolled. Titchy rolls 5 on his d12 and Bull rolls 3 on his d8 - Titchy has initiative. He decides he's going to make it a contest of Skill. Both players have a Skill of d10.
Round 1 starts. Titchy rolls 10 and Bull rolls 9. Titchy has won but not definitively. Next round, he gets to roll d10+d6, and Bull must stick with d10. They roll again. Titchy gets 9+5 on his d10+d6, making a mighty 14. Bull needs to get at least a 7 to stay in the fight. But he rolls a measly 1. He is tossed onto his back and Titchy wins to fight the next challenger.
Mammoth is fighting Baboon. Mammoth has Strength d12, Speed d10, and Skill d8. Baboon has Skill d12, Speed d10, and Strength d8.
Initiative is rolled. Both are rolling d10s for Speed; Mammoth scores 2 and Baboon scores 10. Baboon chooses Skill.
Round 1. Baboon rolls 8 on his d12. Mammoth needs at least a 4 on his d8 to even stay in the fight. He manages to get a 4, just barely surviving. But next throw Baboon will be rolling d12+d6 and Mammoth will be stuck on a d8. They roll again. Baboon scores a pathetic 1+2 making 3, and Mammoth scores 3, matching it. It's a stalemate and neither player can add a d6 next throw. Baboon is back to d12 and Mammoth is back to d8. They throw again. Baboon gets 7 and Mammoth gets 5. Baboon is the winner, but not by enough of a margin to defeat Mammoth outright. It is the end of the round.
Round 2 now begins, with Mammoth and Baboon both again rolling d10 for Speed to determine initiative...
You get the idea. Full disclosure: the crab fighting rules are partly a bastardization of the combat rules for In A Wicked Age.