sounds like a fair rule,
but no, I would not assign an attacking and a defending team. It will give one team "a license to camp", if both teams start with a little amping, which is normal, in the end, they'll get closer and closer. But if you say one team defends and one team attacks, the attackers will have to attack, while the defenders don't have to do anything. Moving up, holding the formation, timing the charge...those are all parts of tactics and strategy, it shows who is the best commander. please don't take that away =)
so far my opinion
btw, when will we know the teams?