your players get slightly worse late in the games because of stamina but the stars represent a lot of different factors that determine how well your player plays in that game, nobody but the admins know the exact formula for it

kengrad wrote: okay thanks. I went cross eyed for a moment when I noticed that my RB, whom had 230ish rushing yards and 5 touchdowns, had a lower rating after the game than he had before.

in general stamina plays a role in keeping the number of stars at the end of the game equal to that at the beginning.
And by the way when you reach huge scores (usually when you are 70-0) against bots/ human teams, the relax rule sets in resulting in all your players "relaxing" and they all have about 1 star at the end of the game(no running up the score after 70-0 )