Incredible Weight is a canon spell. Armor would probably deflect most melee attacks, assuming your character was unarmed. It's not godmoding unless they're giving you absolutely no way to resist, however it's also godmoding if you logically wouldn't have a way to resist (for example, no magic to resist a Brown Way spell like IW) and do anyway.
As for how RP combat works, you want to make the attack without implying or outright stating you've hit the other person, and leave them room to react to the attack. You also want to take into account common sense (an unarmed character in nothing but a loincloth is probably going to lose against a character in armor with a sword unless they're a powerful mage with quick reflexes).
RP combat between OOC strangers is generally a bad idea in my experience, though. It usually leads to complaining like this, or the IC fight degerating into an OOC argument. The best way to go about it is RP with someone for a while, learn their style, and if your styles and OOC personalities mesh decide whether an IC fight is going to work or not. Then again, this is coming from someone who doesn't usually like playing fights.
