It is a sport in which you climb on trees, and the trees are bounded by ropes, bridges in wood, sometimes you have to get through barrels hanging in mid-air. It is some kind of obstacle course. But it is not really a race. But you can make it become a race if you like. You are off course bouded to the ropes. You have two rope around your waist, and a crab at the end of each rope. You attach those crabs to the ropes of the trees. Then even if you fall, you don't kill yourself. You must always be bounded by at least one crab!
It is a very physical sport which demand to be quite tough and a lot of attention. When you watch it from below, it seems easy and funny but when YOU are on the trees, you realize that it is quite tiring. But it is really amazing and nice!