People do gamble on games they know nothing about all the time and funny enough we do bet on games we know but on leagues we do not know as well. I have gambled on soccer bets so many times at leagues I have never watched in my entire life. There is no specific reason for something like that, sometimes it is a promotion, sometimes there is nothing better going around, or sometimes you simple see 3 games from very favorites and think maybe you should do a multi and get a decent return while waiting for other games. So, you could gamble on games you do not know, or you could gamble on the game you know but to teams you do not know about, both could happen very realistically. There is nothing wrong with that as long as you have fun wagering.
Yeah, you don't need to personally do the sports to be able to gamble on them. That makes no sense at all to me, I have never played any sports professionally in my life, I have played a bit of basketball in some youth teams but never graduated to full team so never became professional but that was just one sport.
And yes I do gamble on NBA a lot but I also gamble on football a ton and never played it, gamble on NFL and never played it, gamble on tennis and never played it (this one I never even held a racket, others at least played with some friends in streets) so as you can see from youth team level of involvement to never even participating once you can pick any sport you want and you can wager on them.
Only thing you need to do is check the stats and read what could happen online.