Basic Running
The ballcarrier always has a circular reticle just behind him. This is what the Player uses to move the ballcarrier.
The active player -- the ballcarrier -- is always moving forward. Think Temple Run/Canabalt.
This means that the Player only controls movement on the X axis:
If the Player tries to move the reticle up or down, it remains locked on the X axis. The reticle is basically a single-axis joystick that follows the ballcarrier around.
Reticle movement on the X axis modulates the ballcarrier's Y velocity:
The Player uses the reticle (plus the constant forward movement) to move the ballcarrier around the field:
The ballcarrier will react to sudden/quick motions with...sudden/quick movements (e.g. jukes, cuts, headfakes, et cetera):
This kind of stuff is all ability/statistic based (e.g. a player with low agility won't cut quickly, he'll just sort of eventually lumber towards the new direction, etc).
If touch input on the reticle is lost (Player removes finger from screen, moves vertically off of the reticle, et cetera), the reticle returns to the ballcarrier's on-screen position...
...where the ballcarrier will attempt to avoid defenders automatically:
MAYBE? I dunno, this part might be dumb. He might just run straight ahead into whatever is in front of him.
Option Plays
On most running plays, the QB will automatically hand off/pitch to the HB/FB. On option plays this is not the case -- an option play is one where the QB has the option to either hand off/pitch or keep it himself:
Here's an in-game example:
There are several permutations of the option concept, but this is the most commonly seen today.
In-game, this is what the Player will see:
If the QB hands off, the RB is now the ballcarrier, and is controlled by the Player. If the QB keeps the ball, he is controlled by the player.
Passing
Passing expands on the option concept by adding multiple potential receivers into the mix.
First off, on a pass play, the camera zooms out:
This gives a bit more room to see what's going on downfield. It also gives the QB interface some breathing room.
Each receiver is assigned a color icon; each of these icons corresponds to one of the QB's passing icons:
This is pretty simple: it's Angry Birds meets Madden: the longer/further the player pulls back, the harder the QB will ultimately throw the ball. A short, gentle flick will result in a softer throw. This affects the trajectory of the ball as well (a flatter, lower trajectory vs. a higher arc).
Extreme cases magnify any shortcomings in the QB's ratings: short swipes/flicks that don't meet the minimum threshold will result in wobbly ducks; a swipe that's held down for too long will be too powerful and likely go nowhere near the intended receiver.
For every situation, pass route, and receiver, there will be a happy medium. All the Player has to do is decide who he's throwing to, touch that icon, pull back on it, and let it rip. Aim, distance, etc. are all handled by the game, under the hood (Madden-style).
QBs will still need to be able to move in the pocket, however:
The QB automatically avoid any oncoming pass rushers back dropping back further -- sort of the inverse of the normal running functionality. Note that this will only happen if the QB is in imminent danger; the player can still dodge normally, on the X axis.
To pass, the player has to move his finger from the movement reticle to the little passing icon -- this 'keep dropping back' behavior might work, or maybe we just have the QB continue, slowly, in the direction they were headed before? This one is going to take some trial and error.
Sometimes the Player just wants to pull it down and run, or scramble. By touching/holding the active player reticle with two fingers, the normal running functionality (always running forward) can be re-activated:
Once the QB reaches the line of scrimmage, normal functionality resumes, and the Player can continue controlling with the usual one-finger touch.
