When I watch football all I see is a bunch of people kicking a ball around (barring the obvious skill of a few people, Messi springs to mind). I’m sure there’s more to the sport, it’s just I don’t know enough about it to tell what’s going on. I think the same applies to rugby, it’s unbelievable if you understand what’s happening, assuming it’s a decent game, but if you don’t know much about it it probably looks like a bunch of large men running in to each other.
That said, I think rugby’s got more of a gladiatorial element to it, so maybe more entertaining than football to someone who doesn’t know anything about either.