The answer to the OP's poll question, taken alone without any other information is NO! There is no legal justification for assaulting someone simply because they were following you.
Now, you do have a right to defend yourself using reasonable force if you have a rational belief that you are facing a credible threat of harm. You can escalate this defense to the use of deadly force if you have a rational belief that you are in imminent peril of death or serious bodily harm.
To address parties on both sides of the case people keep citing, here is a HYPOTHETICAL scenario.
You are a young individual visiting a location you are not very familiar with, although you have a right to be there. It is night time, and raining, and as a typical youth you would be experiencing a heightened awareness of your surroundings because you are alone in unfamiliar territory. Compound this perhaps by prior nighttime encounters with other aggressive kids, and/or perhaps being rousted by cops or other adults.
Now you notice someone seems to be following you. You begin to make efforts to lose this tail, cutting accross lawns and through yards. You don't think the person following you is a policeman because you know they are more open and aggressive, usually shining lights or turning on their flashers and using a loudspeaker to ask you to halt. Your apprehension is increasing because you don't know who it is or why you are being followed. NOTE: the person following is a concerned resident who thinks the teen's evasive actions are very suspicious. This increases HIS alarm, and his desire to make certain the individual is not a threat to his neighborhood. He keeps following.
After a period of "cat and mouse" the two meet. Question: What if the concerned citizen steps up and grabs the arm of the nervous teenager to try to stop and question him? Can the teenager strike out in honest fear he is being assaulted?
My point is, we don't know exactly how this particular confrontation started, right? I have not followed the case so I ask; was there any other eye-witness to the start of the fight besides the survivor? My understanding is that the survivor of the confrontation never testified on his own behalf, so we only have his statements during his police interviews for what happened initially, correct?
So I ask again, would any teenager caught up in such a situation have the right to strike a person who has been following him if that person grabs him first?