In territorial species, it is sometimes less costly to help a neighbour fight off an intruder than to re-establish territory boundaries with a new, potentially stronger neighbour. In fiddler crabs, a male resident will only help his neighbour if he is larger than the intruder who, in turn, is larger than the challenged neighbour. Does this influence with whom a territory-seeking male decides to fight? I show that territory-seeking males appear to choose opponents based partly on the size of the resident’s nearest neighbour. By avoiding challenging resident males with larger neighbours, territory-seeking males can reduce the likelihood of initiating a fight with a resident who might gain help from his neighbour that decreases the likelihood that the intruder will win the fight.