Clubs are a new thing introduced recently to League of Legends as a way to let people group together. In the beginning you might have joined some random group or were invited to a group and now you’re not sure how to leave.
First, log into the client, go to the right-hand corner and next to your friends list will be an icon where you can check on your clubs and chat rooms. Click the group that you want to leave, and this will cause the group chat to pop up. In the right-hand side of the chat, scroll through the members list until you find your name. Right-click on your name and you’ll see the option to leave your group.
Once you click on ‘Leave club’, a little prompt will pop up to confirm your decision. Click on ‘yes’ and then you’re done, if it is your own club that you’ve made and no one else is in it then you can simply go back to create another club and enter the same name, and this will put you in the same club as before. If it is another club by someone else then it’ll be a bit harder because you’ll need to be invited back to the group.