Well I think I might have to try and keep myself short winded here too, but we'll see how far two cents goes.
If you date back most contemporary sports, you end up in a time period very different from today's. Most notable is that there's little to do aside from work, eat, and sleep. Now recreation is going to be something interesting when added to that equation. I'm sure it can be an easy mixture of alleviating boredom and enforcing competition. That alpha dog instinct is apparent in the human species, so it's easily said that our desire to rise above others is cause enough to compete.
The trouble with any one sport is that it's very focused. Specific rules make for specific games, which make for specific competition. One who's good with their feet may excel at soccer, while someone more coordinated with their hands may excel at baseball, or say, volleyball. Perhaps that combined with the desire for variety is the reason we see so many versions of athletic display these days.
Now as for the modern day, there's something more to be said about that. Upon any new discovery comes excitement. You play for the thrill and enjoyment rather than purpose. It's not without time that we begin to see the benefit that comes from something thought great for it's sheer existence, like the health benefits of a glass of wine. Sports have basic life lessons applied to them, which are often overlooked in the excitement of it all, but they're there. Teamwork, discipline, strategy, quick thinking, fitness and grace in victory and defeat are all things that should be held in practice, and sport proves to be a bountiful source of all and others. It's no surprise then that children make up the majority of people playing sports these days. It's unfortunate that not all will take with them all their is to be had.
Analog's underwear are digital. right now they're set to inverse 1 (I think that means they're on my head).