"No matter how you slice it?" Maybe no matter how YOU slice, it, but I define "force" differently, and slice accordingly. Anyone can walk on any public street. Barring the existence of a restraining order, anyone can follow anyone from a distance if they so choose. One may find being followed annoying or discomfiting, but I can't see how it can reasonably be defined as force, or more aptly, violence, against him. Punching someone in the face however, unequivocally is.
If someone were to follow me and I confronted him, I might ask strongly "why are you following me? Who are you?" etc. If they replied that they were with the neighborhood watch, keeping an eye out due to recent burglaries, I might say "thank you for helping to protect our neighborhood! I live over there at [address.] Have a good night." And walk away. Or maybe I would ask him where he lived and name some people we might know in common. Maybe I would offer the watchman to walk with me to my door. Maybe I would offer him some of my skittles. One thing I would certainly NOT do, unless physically assaulted, would be to put him in a ground-and-pound, which, if you have any fight training/knowledge at all you'll know, is in fact a deadly position.
In the very realistic and reasonable alternative scenario above, where is the force/violence? Clearly, there is none.
Treyvon certainly could have chosen that kind of rout - but that is not one that would satisfy the macho ego of any young man looking to prove his toughness to himself and the world.
Throwing a punch instead was obviously an immature emotional decision, and the outcome was tragic. We've all done stupid things in the process of growing up, and it is always tragic when a young person pays for one of those stupid things with his life, never getting the opportunity to out-grow the internal motivators behind it. But when that happens, and said youth has chosen to pose an imminent threat to the life of another, the target of that threat cannot be legitimately blamed for the tragedy.