I have read that the physical description of the two people is as follows. The person shot was 6’3”, 150 lbs and 17 years old. The man doing the shooting was 5’9” and 200 lbs and 28 years old. Without a weapon, who was more likely to be a physical threat??
Bruce Lee weighed 135 pounds at the start of his fighting career, eventually getting up to 160. Would you consider him a physical threat without a weapon?
Heavyweight champion Jack Dempsey was 6'1" and 150 pounds as a teen, when he started his boxing career, and routinely beat men much heavier than himself. Would you have been interested in getting into the ring with that skinny little guy?
Trayvon's weight has been put at anywhere from 150 to 190, depending on the source. The definitive source would be the autopsy report, but that's not been released for some odd reason. The bottom line, though, is that a lot depends on the relative physical condition, training, and fighting experience. Zimmerman had more weight, but much of that appears to be fat. Martin had more reach, and probably more speed.