The thing about magick is in reference to defense you can't use protection, spells, barriers, etc... to protect against physical danger in most cases from what I understand. A normal human can't manifest a barrier strong enough to block something as solid and as fast as say a bullet for example. Magickal defense is normally used to defend against malicious magick. As for attacking I don't know much though sending someone flying or something similar isn't really possible and even if you could someone would bring up ethics. In the end I think it's fine to defend yourself if you need to by any means if your life is in danger and you feel you have no recourse, but it's always best to think before you act of course. I sound like a after school special sorry.
Many martial arts teach how to use and direct energy (qi/chi) into your strikes. Tai Chi and is big on this. They practice slowly to feel the energy flow and focus on it. Sped up, it packs a lot of power.
This is why martial artists yell when they strike. Its a way of forcing more energy through the use of sound.