Roll damage for one member of the mob or squad - all mob/squad actions are done by one member with the rest assisting, essentially. The benefit of the mob/squad is that because the others "assist" the attack, this makes it more likely to succeed and more likely to generate Momentum (which can, in turn, be spent to boost damage).
To his friend a man
a friend shall prove,
To him and the friend of his friend;
But never a man
shall friendship make
With one of his foeman's friends.