It is a depth chart...starters(1st) to backups(2nd) to reserves(3rd).
Depending on how you set your "Substitutions" option is how the players will be played. For instance if you select "Let Coach Decide" as your "Substitutions" option then the game will start of with starters but the coach will put in the best player for that position regardless of how you set your starters, backups, etc. Normally though the coach will first go to the backups before going to the reserves. But if Player A(starter) is in foul trouble/not playing well and Player B(backup) isn't playing well either then he may go to Player C(reserve). If Player C plays well then he will get the majority of the mins even though he is a reserve(3rd on depth chart). Basically the coach picks the player with the hot hand to play no matter where they are on the depth chart.
If you pick "Strictly Follow Depth Chart" as your "Substitutions" option then the coach will always sub in players in the order that you placed them on the depth chart even if they aren't playing well. This is a good way to make sure your younger players and players that need mins play. With this option your reserves will hardly play unless the starters and backups get injured or in foul trouble. In my last game, my reserves got 2-5 mins of playing time. Backups would play for temp. breaks.
I'm not a developer so maybe I'm wrong. Just what I think
