1.If you are a member both in league and on battlefield, you can quit your league directly.  
2.If you are leader in your league, you need to transfer your position on main screen to another member before quitting your league.
3.If you are chief commander of your field, you need to transfer your position on the battlefield to another member before quitting your league.
4.You can't quit your league if you are in league battle. 
5.If you are in a league team preparing for league battle, you need to quit that team before quitting your league.