You want to sanction all your players, but for one specific league only?
Go to Player Sanctions (Menu > Manage > Players/Teams > Player Sanctions)
1. Choose the league you want to sanction.
2. Hover over the word Is Sanctioned and right click on your mouse. (this will give you the options to Check all)
3. Select Check All.
*You can also choose multiple leagues at a time. (See image below)
You can also choose multiple leagues at a time. This will filter and only show players from those leagues.