Currently, you are only allowed to control the offense. The defense is controlled by the computer. The lone exception is on an interception or fumble recovery, where the player then controls the defensive player who has intercepted or recovered the fumble.
When a change of possession occurs, you take over the other team, and go down the field in the opposite direction.
During game play, you control the player with the ball. That player runs at the mouse pointer. Thus, move to mouse to where you want to go, and the player will try to run towards it.
Other players move based on their pre-specified actions. Examples include running a pattern, pass blocking, run blocking, etc., on offense, and chasing ball carrier, lateral pursuit, covering a certain player, etc., on defense. Check out the 'player_create' and 'player_move' in 'player.tcl' to get more details on this (especially of interest if you design your own plays!).
The ball is hiked by pressing the left mouse button. Then the action begins, with you as quarterback. To handoff, press the second mouse button when you are "near" the designated hand-off target.
To pass, hold down the first mouse button. Then, aim the cursor to where you want to pass the ball. Let go of the first mouse button to pass. The nearest receiver will automatically run to the ball. Timing is everything! You can also pitch the ball in the same manner, but a bad pitch will result in a fumble (as opposed to an incompletion).
To punt, press the third mouse button. This works at anytime during normal plays.
To select different plays, use the second and third mouse buttons to go up and down in the play count. The status bar at the bottom indicates which play you have chosen, as well as the down, and the time remaining in the game.
You can design your own plays. Checkout 'standard.pb' for some examples. Currently, there are 12 offensive plays, and 5 defensive ones. The defensive play is selected by the game, and uses a simple randomized algorithm to pick the play.
Each player has different speed, acceleration, and strength characteristics, as defined in the team files. 'team.tcl' loads in a team from a team file (e.g. 'standard.team'). Speed determines the maximum rate a player can move, acceleration determines how quickly they can change direction, and strenght determines how many hits they can absorb before getting tackled.
There is also a sound option, which narrates what is going on in the game. This uses the program 'aplay' to announce yards gained and so forth. The computer voices were generated from the site 'http://www.bell-labs.com/projects/tts/voices.html' (check that out, it is cool). Look in 'sound.tcl' for more details. Note that sound is off by default.