JJM, I knew nothing about rugby until my son started playing. I quickly became hooked.
Chris had a HS rugby coach from England who played top flight rugby in the 70s. He was a huge England supporter--it was always a regret that he didn't play for England. (He is also a portrait and landscape painter in high demand. What a combination!)
So, I started watching Rugby just as England won the World Cup in '03. Man, the last 2 games against South Africa and Australia were intense!
For several years, you could get Setanta sports on DirecTV. They showed all sorts of sports--football (soccer), Celtic games like hurling, Australian football, etc. And they showed a lot of rugby. I could watch the English Premiership, what is now the Pro12 (Irish, Welsh, and Scottish clubs), Super 12, Southern Hemisphere rugby, and international competitions: the European 6 Nations, the Southern Hemisphere battles between SA, Aus, and NZ. In '07, I saw all the pool world cup games I wanted to see and was gutted when England came up a bit short in the final. Damn, that was fun. That service is gone now, however, and I haven't been able to follow Leicester Tigers for years.
I have said on other forums that any American football fan should give rugby a serious look. I promise you'll love it.