If you want to try things out, for example seeing how some offensive plays work against defensive formations, it's difficult to do so - you can't fully engineer those situations in games as you've no control over opposition rules.

An idea might be to allow on non game days a team to define specific scenarios, say a max of 20 plays.

Interface could be :-

------------------------------------------------------------------------
| DOWN | DISTANCE |
| OFF PERSONNEL | FORMATION | PLAY |
| DEF FORMATION | DEF PLAY | ITERATIONS |
------------------------------------------------------------------------

So say 1st down, 10 yds to go
I Formation 3 WR, FL Hitch or whatever
Nickel Normal, Double WR1, 20 iterations.

Allow at most 3-5 scenarios to be defined. Players used would be those used as if game being played, so would include overrides - your offence vs your defence. Injuries disabled for these plays. Allow at most 20 iterations of a play; say a max 50 plays overall for a session.

Using the above example, you'd get into in the following form where the text would be similar to existing match play text.

---------------------------------------------------------------------------------
| ITERATION | YDS GAINED | TEXT | VIEW |
--------------------------------------------------------------------|------------
| 1 | 4 | X passed to Y | |
----------------------------------------------------------------------------------
...
--------------------------------------------------------------------|------------
| 20 | -8 | Intercepted | |
----------------------------------------------------------------------------------

To save server space, these practice session plays should have a limited shelf life to be available - maybe a week?