Is it possible to call ban_user function from theme functions file?

On my theme, when a users role changes to a custom role called nobueno I take care of some additional administrative tasks. When this role is added to the user, the user is removed from all buddypress groups and all roles except nobueno. I would like to ban the user without having to make this additional update on the user’s profile. Can I call the ban_user function from within my theme’s functions file? If so can you give an example?