Tommy effectively nailed it. Love or hate them, sports are the single most universal "shooting the shit" topic that most people can get in on.
Rachel's dad is a staunch conservative Republican who is homophobic, a slight bit racist and all kinds of other shit that would effectively scare the piss out of me, but I'm able to actually sit in the dude's house with minimal discomfort because we can at least talk about sports.
My gramma and I constantly talk Red Sox. This is how we always connected growing up and to this day, she's one of my primary influences. And ask anyone who's met her, my grandmother is the absolute shit. Shane and Rachel can both vouch for this.
It's also one of the primary ways I've been able to connect with my brother in recent years. We're both incredibly different people and most of the things we have in common are more our failings than anything (Crude, tactless behavior, very stubborn, we hold terrible grudges), but we've always been able to connect on sports, at least.
I actually only ended up on this forum because of sports. Shane and I met through a Red Sox forum and he turned me on to this forum.
Sports is the tried and true uniter. There is not a single subject that ranges so many different classes, cultures and races. Until recently, the only really large group that you couldn't just strike up a conversation about sports with was women, and that's changed substantially over the past couple decades. Politics, video games, books, movies, music; none of them are quite so wide ranging and easily relateable as sports are.