So today I found this article (courtesy Sesquipedalian) about the Spy’s backstab mechanics. It’s an interesting read, though I do wonder how the author figured out the hitboxes and “hulls” mechanics, as it seems like something that would be impossible to determine precisely through in-game testing. Does it show such things in Hammer or other programs?
Something that the author says at one point is that “the angle calculation [for backstabs] has nothing to do with the player model, and everything to do with where the victim’s crosshairs are pointing at the moment the spy attacks”, which makes a lot of sense in terms of keeping as many players happy as possible, as it lets people not worry about what they look like in-game (their player model) and focus on their playing. Just a little thing that came to mind when I was reading. Another issue that came to mind is Valve choosing to use the hull boxes for melee hit detection as opposed to using the usual bullet hitboxes. Is this a good idea? It doesn’t make a ton of sense visually, but then again, if the player collision detection is being decided by these hull boxes, then the weapons that function by colliding with enemy players should also depend on them, right?
On a completely unrelated note: If your parents ever say that they’ll buy you a laptop under the condition that you don’t take your desktop home with you during fall and spring breaks, consider carefully the pain that those long weeks without TF2 will bring.
What am I supposed to do, homework? Pshhhh

The reason why it’ll be more difficult for a hitbox melee mechanic is you’ll have to be AWFULLY close to the person. Melee swings would require you to be very close. Also, it would be very frustrating if you were to swing and hit just underneath the arm even though you were right next to them. I think the hull mechanic is good.
This video (music is horrible imho) shows what the article was talking about being able to hit from the right side better. The theory of the video isn’t too spot on, but you technically can still hit the “front” of someone on the right side more than the left.
http://www.youtube.com/watch?v=FeiVxNjMIrI