We have a little walled playground near our house - little climbing frame, slide, stepping stones, toddler swing, very clearly aimed at a young primary/pre-school audience.
It's currently being completely taken over by a huge group of 10-12 preteen/early teen boys playing very rough games of football with real leather footballs. The bang the balls off the walls and hoof them in the air so they go careering everywhere at speed, they run around roughly after the ball pushing and shoving each other and getting in other people's personal space, they fight and shout aggressively and swear. Not a parent in sight of course so no-one to appeal to to get them to moderate their behaviour/find a more suitable venue (like say the massive park 5 minutes walk away). I've had a word now and again but generally just get mutinous stares and/or backchat. I can't really take my kids (2 and 6) there to play any more as it isn't safe for them and the atmosphere is so aggressive.
Why do people just turn their kids out of doors with no idea where they're going/what they're doing? It makes it impossible for other parents - either they have to tell your kid off for you (immediately in the wrong) or they simply have to either put up with inappropriate, loutish behaviour or give way to it and leave.