Yep, it could have played out this way. A 17 year old kid who weighs 150 lbs and was carrying a soft drink and pack of skittles (see here, no weapons) might have just attacked a 250 lb man in the dark, while running away and crying out for help. I guess anything is possible, however unlikely. But where would you place your money?
Unless Zimmerman beat himself in the face and fell down in the grass on his own, I'd say Martin had it in him to fight.