I've found trees that were knocked over when young, but continued to grow, like a tree pushed over by a flood. The smaller branches on the side and underneath such a tree tend to turn upward toward the sunlight. As they grow, they become big enough for club handles. By cutting the main trunk on either side of these upward growing limbs, you wind up with a roughly cylindrical head on a properly curved handle, just ready for carving into a traditional ball club. I think producing a club in this manner would have been easier for stoneage indians. After contact with whites, and steel cutting tools becoming available other methods of production would have become easier. It would be intersting to see if there is some correlation between the existance of the ball headed club and availability of steel tools.