a little more background about NBA ref's
http://www.probasketballrefs.com/Default.aspx?tabid=68
Q. I know the refs are full-time, but do refs have other jobs? How many hours in a week do you spend officiating? What do you do when you’re not in season?
A. Being an NBA official is certainly a full-time job. We typically have 2 to 3 games a week, so we’re traveling all the time. You could be in Dallas on Tuesday, Atlanta on Thursday and in Los Angeles by Sunday. When we’re not in season, we spend our time at clinics, training camps, watching films of games, and studying the rulebook. Some people have some personal business on the side, but being an NBA official keeps most of us very busy.