Having a ball?

last day went popular in jusco, i'd learned an interesting english that we as local ppl wont used to to it. It's 'im having a ball'.well, this does not mean that im really having a reall'ball'.Instead, this ball in this sentence bring the meaning that, im enjoy it.....or im happy on it..something like that. So, normally for the English ppl, when u ask them how's ur trip?maybe they will asnwer u 'well..im having a ball for the trip....anyway..it's quite funny for me.....=_=