Hi , this is a tough one ,but i think it comes down to symantics , offense - defense , there all the same , I think the real question is when do you react to someone infringing on your personal space and rights , the answer for me is straight away.
No one has the right to make you feel uncomfortable or threatened , If they do make them aware they are ... tell em to back off .
There response will make it obvious of there intentions .
what s defense ? , i believe it`s taking away the risk , making it so the atacker canot harm you , this in my minds a good offence , stop impair the atacker so he cant attack no more

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If anyone thinks you can block restrain your opponent into stopping your better than me , these things often just give the attacker an opurtunity to start again . Most restraints etc need a good offensive move to set up IMHO against an uncooperative assailent .
I wish the world was`nt like this but im afraid it just might be .
Stryke