Can only select a drop down option once

I had a look at that and it wont work as the players below are allowed select the same team as any other player. They just can not select the same team the next week.

I've attached my spread sheet. I've just added 3 players and I added all the teams. I've listed all the teams in column Z this time ( no reason )

would the code have to 1st check the players selection.... then check the list in col Z then figure out what is left for the player to select ?