When I walk to my local farmers market, I pass by a corner which has some sports facilities for a college. Often there are organized events going on, but sometimes there are informal ones too.
For example, not long before Halloween on the baseball field these guys got together to play in costume. I have no idea if this was some kind of frat initiation rite, some kind of intramural game, or possibly a sports team doing some kind of bonding event.
A few weeks later, cricket players were playing there. I watched for a little while, and I think I actually started to get the hang of the game a little bit, which had previously completely escaped me.
And now this winter, next to the baseball field, the college set up an ice rink with free admission to anyone who wanted to get in line.
One fun thing about cities is the big variety of things that can happen in just one place. On the fields where my son once played youth soccer you could also come across softball, rugby, flag football, lacrosse and ultimate frisbee. I never saw kickball, though.