Good post Lanefan! Only have a few minutes so I'm going to have to do this piecemeal, starting witht eh NFL stuff.
I know nothing about MMA so I can only take your word for this.
Not necessarily. Receivers often run their routes with a "cut" because that's what the called play expects them to do. Running backs just try to go where the defenders aren't; quite different than most D&D scenarios where the intent on both sides is usually to engage. Probably a better example here would be what happens right on the line of scrimmage, about the closest thing we have to melee combat in the modern world.
But even without that, while the presence of Kam Chancellor and-or Earl Thomas in the backfield may influence your choice of path as a running back, that's all it does: influence your choice. They're not forcing the RB to go somewhere else; the RB could choose to try and run right at one of them with a straightarm, for all that. So, no forced movement here; just more data to process when choosing where to go.
I chose WRs and RBs versus the "back 7" of the defense (unless you're playing a 3-4) because I wanted to work out the dynamics of "martial forced movement at a distance." The guys in the trenches have both contact and "martial forced movement at a distance" (when the D runs stunts or the O runs a Trap play or pulls a Guard or Center on a Counter or Sweep), but, as you noted, most of it is basically intimate, up-close-and-personal.
So the basic "in-cutting" portion of the route tree includes Drive, Slant, Dig, Hook, Post (as below).
Plays, of course, are scripted and have very specific things they are attempting to accomplish versus specific defensive concepts. On a pass play, each route is challenging either a specific player or area and thus "forcing" the defense to respond.
For instance, a "4 vert" concept (combo routes of 2 seam/skinny post routes + 2 fades on the boundaries) is designed to put maximum stress on the 2 Safeties and force them into a catch-22 decision ("stretching" the field vertically and horizontally simultaneously). Depending on how these route combos influence (eg force them to move) the safeties, the QB will make a post-snap read to either throw the seam/skinny post or the fade.
The same goes for play-action passes. Last week, Mariota gashed the Tampa Bucs with Read Option Play Action from the Shotgun and 4 Vert passing concepts. On their first touchdown, play-action pulled in a rookie Middle Linebacker for one or two steps (forced movement as he crashes the line of scrimmage), and the combo route on the outside forced both Safeties to go wide of the right and left Hash (as he went after the Fade route on the boundary). Boom, he throws the Skinny Post (to Kendall Wright I believe) over the "sucked-in" MLB and now the out of position Safeties each has a bad angle of pursuit because they were "force moved" by the boundary Fade routes. Kendall Wright takes it to the house. 3 defensive players "martial force moved at a distance" due to (a) play action fake to the RB from the shotgun and (b) the boundary/hash route combos.
That is all the time I have for now.