I don't know how GZ got a straight scratch on his nose by being punched but assume more will come out at a trial. Hopefully his statements to LE will be released long before that.
I believe all of us would be relieved and have high praise for any 17 year old kid managing to get away (by fighting) from a stranger whom the kid had no doubt was following him/her and didn't know why. To my knowledge GZ did not identify himself. Trayvon stood his ground.
Someone else pointed out, and I agree, they don't look like scratches. They look like broken blood vessels, with a little bit of blood pooling on the right. Like what you see here:
I'm not a medical expert - far from it - but I can certainly see how those "scratches" aren't scratches at all.