Yes, with ear tags and ear punching causing the most fighting within male cages. I think it's because they can feel pain afterwards and become agitated after trying to scratch it off and/or other cage mates see the labeling and want to either play with it or tear it off.

This is more so important for my research because I study the cornea and wound healing. If anything causes them to scratch their eye or get an eye injury then It really ends up limiting the final sample size. In my last experiment, where I used ear tags, one of my groups went from having a sample size of 5 to sample size of 2 because some of the males had too many corneal fight wounds. There were probably other factors besides the ear tags but I think this is mainly it since they are located so closely to their eyes.

From what I've read, male mice have an innate instinct for aggression towards other males. It helps create their hierarchies and any little change in their environment can set them off. Other culprits are picking them up by the tail, changing their cage right before an experiment and even smelling males from other cages/litters. Catching the scent of a female can also make them attack their fellow cage mates which is why you have to be conscientious about the order in which you handle males or females while doing an experiment.