You have to feel safe enough to play – physically, mentally, emotionally, socially, environmentally safe. And you have to feel that you don’t have to play.
Note the italics on the word feel. As bungee jumpers, rock climbers, skydivers, parkour runners, cancer and tsunami survivors, Palestinians and Israelis can tell you, it’s more about feeling safe then about actually being safe. Another reason you feel safe is that you you know you can quit whenever you want to. Not that you are going to quit. Just that you know you can.
One of the things that helps make people in a play community so playful is that the whole community works together to create that sense of safety. More than being there for the fun, they are there for each other. You can say this about any community where people feel safe enough to play together, to sing and dance together, pray together, build together, to let their chickens and children roam free. They are there for each other when needed, and, for the rest of the time, for the sheer, divine fun of it all.
For more about safety and fun, see this.