free agent 
noun
A person who does not have any commitments that restrict their actions.He allows her to travel with him on the condition that it is a temporary arrangement - that he is a free agent and is not in any way committed to her....
- The dot com revolution spawned a whole new generation of savvy, job hopping free agents who each said proudly they were their own security.
- However, we should keep in mind that Senators to some extent are free agents.