In order for Zimmerman's defense to use it as justification for shooting Martin (and make the jury believe it), yes... they have to prove that Martin was bashing his head into the pavement. At the very least they need to prove that it *could* have happened, but with something more definitive than "hey look at these scratches on the back of his head".
As far as my intelligence goes... I'll let my points speak for themselves. My deepest apologies if they're a little too complex for you to grasp; but unfortunately for you, I cannot pander to the lowest common denominator on a regular basis. But, I to brag just a little bit; I graduated high school at the age of 16. No, that doesn't say a whole lot, but it should prove that I'm just a bit more intelligent than your average person. But, that's not to say that we don't need "average" people out there. I'm sure you do a great job in whatever menial labor position it is that you hold down... we need people like you, be proud of yourself.
Question, if I bother you so much, then why do you keep responding to the things that I say? Oh, that's right... you're trying to get my attention, so I can be the father figure for you that you apparently never had.
Oh, and if we want to use decimal points, then it would be 157.0, but since they only gave the score to me as a whole number, I figured the ".0" tacked on the end was a little redundant.