on the fly subs is great, they just don't explain it well
1. down on the d pad will bring you to on the court players
2. Use Right Stick for corresonding player you like to sub out point guards are up on the right stick shooting guard down follow the on screen diagram next to their name. Once you select the player you want to sub the next screen is the bench
3. Now using the right stick chose a player you want to sub into the game
4. Press circle to confirm changes and you're done the player will walk to the press table.
What I would like for them to do is use some confirmation colors like when you select to sub out the players name will turn red and the player you want to sub in will turn green. Right now there is no way of knowing if you're doing it right unless you tinkered around with the mechanic.