Whether it was with predators of another species or rival tribes, I think in group camaraderies and out group hostilities were very common and very necessary in paleo times (and we see remnants of them today in rival religions/political parties and such). I also think minor injuries are a good thing on occasion, as they strengthen the body and replicate the conditions we used to live in. Too cushy and we get soft!
How many of you know how to defend yourselves with your bare hands and/or weapons? Do you train for such activity regularly to keep your refelxes sharp? I think these are very important skills to know, whether or not we will ever need them. Exuding confidence is 99% of the game. If you were attacked by man or animal, how would you react? I would turn and face an equal or leser opponent. I might warn first or just counter depending on the situation, but I would certainly not fear. Fear is the mind killer ... If I faced a bear or worse, I would crouch or possibly run. But the training is so important in order to know the difference and act nearly instinctually.