A club's Owner can hand that role to any existing Club Admin at the club at any time. This changes who has ultimate control, including billing, so Dugout asks for a deliberate confirmation step, like typing the club's name, rather than a simple "are you sure."
You're required to transfer ownership first in two situations: leaving a club you solely own while others are still members, or deleting your account under the same circumstances. In both cases, a club can never be left without an owner.