If a player is listed on the wrong team it is easy to remove them. When you delete the player you are only deleting them from that single team page, you are not removing them from the entire system. Therefore, if that player is listed on other team page's he/she will still appear when deleted from a different team page.
In admin mode get to the team page. Either login as an administrator (elements > team pages > click on team name) or login to the team page as a contact.
Click on Roster (in green bar at top of page)
Find player in question, click the red X on the far right of player's name
Confirm that you do indeed wish to delete player