Will a rat hurt an injured rat?

This very much depends on the gender, and social situation. Were these rats living together? If not, there is a high chance of the advantaged rat attacking, as this is highly likely to happen regardless of whether or not that rat is injured. Two Male rats are far more aggressive towards each other if they have never met, as both are fighting to be the dominant . Two females may fight too, regardless if one or the other is injured. Females tend to be more active and jumpy, while males tend to be lazier, but more aggressive.