Obviously neither one of them acted appropriately. This is a situation where you have to ask yourself a simple question. If I was the E-5, would I want someone to explain what happened? Remember doing the right thing is sometimes tough. Is it fair for the E-5 to get an Article 15 for disrespect and the E-6 to walk for assaulting the E-5 and breaching his personal integrity? While I’m sure the last thing you want is more conflict, I believe the best action would be to inform the chain of command of what happened. Otherwise, you allow the chain of command to make a decision without all the facts, and allow a wrong to go unchecked.