Every once in a while I hear about this or that athlete choosing Wales or Scotland over England for the national side in football or rugby. Prominent examples that come to my mind are Ryan Giggs and Gareth Bale. I'm not sure how the regulation is with regards to the national team eligibility, do all citizens of UK have the liberty to choose any national side (in the UK that is)?
As a follow-up question, isn't it a bit tricky that UK is represented as one single team in some disciplines (e.g. track and fields) and as individual "nations" in other disciplines (e.g. football or rugby)? I mean, that could technically mean (or at least extrapolated to) that individual states in the U.S. could also have their national teams?
Could someone with more knowledge on this matter, help me (us) figure this out? :)