It's simple enough, tsuwm. You make all (or most) of your income at whatever it is (assuming there are those who do it for the love of it) you're a professional, if you do it entirely for the love of it you're amateur. If you make a large portion of your income doing it but another large portion doing something else (say, selling cars) you're a semi-pro. Semi-pro baseball used to be a big thing in this country. Every little business had its baseball team, some rivalled professional teams. But then, some companies hired former greats for their baseball talent and gave them night watchman jobs that they could sleep through just to have them on their teams. It has nothing to do with quality of talent but it is easy enough for someone to caste aspersions (before or after swine) on someone who doesn't make a living wage at a sport, thus making amateur a derogatory term.
