It is used on the shoe soles in classical dancing. Sports use it to grip baseball bats and tennis rackets, pole dancing and pole vaulting to drastically improve grip hold.
It comes in yellow translucent crystals or rocks that powderize under finger pressure. It could be mixed with chalk or magnessium.
Dangerous? well, if you eat rosin it can makes you quite sick. (Same if you melt it with a torch on your hand or blow it on your eyes!) Otherwise brake the little cristals on your hand and rub the grip with it. The skin warmth melts it and the stickiness lasts for a couple of hours. Cleans with soap and water.
If it gets wet, dry it with a towel and it becomes even more sticky, or add a bit of chalk. It hasn't been tested under heavy rain (probably nothing works when the towels get soaked), but with sweat or a bit of water it's fine.