In this world of urban sprawl and obesity I want to draw people's attention to urban bike polo!
http://www.bikepolo.ca/I'm by no means an organiser nor a top player, but I do play whenever I get the chance. (I have tonight off work so I can finally get myself to a nigh match!)
I think that it's wonderful because it's essentially a sport that can be done in the middle of the city and with minimum equipment. Many people already own bikes, and mallets are often shared.
It's a way to get out of the house and get the blood flowing and a chance to play something as a team, in cities where I think too often people keep to themselves and lack the community of more rural areas.
The group I play with are very respectful of all ability levels. The serious guys will play hard with each other, but as soon as a beginner rides onto the court, they'll back off. Similarly, some of the guys have bikes specifically for polo, but they respect that other people will have to ride their bike to work the following day and therefore can't have it damaged.
It's all about the level of seriousness that you want.
There's even world championships for the (original) grass version
http://www.worldbicyclepolo.com/I see this as an evolution of sport to suit our largely urban lifestyles. So
find a club in your city or if there isn't one,
make yourself a mallet, grab your bike and some mates and get a game started!