Offensive = attack, aggressive, to cause pain/suffering, etc.
Defensive = defend, protect, to prevent pain/suffering, etc.
Many martial arts are defensive arts meant to protect you from offensive people such as street thugs and other criminals, so even things that may seem offensive and can be used offensively may be considered defensive according to your intent. What you have mentioned here, judging by the intent mentioned, is defensive and not offensive. If you were to teach people to strike first and/or without mercy that would be more offensive. Learning to shield, block, deflect, etc, anything that keeps you from being harmed is defensive even if it sends the attack back to your attacker causing his desired effect to occur upon himself.