The ball displayed here is a silver replica of a kaats ball, which was put up as a prize for the winner. If you look closely, you can see the flag flying from the tavern, as a sign that something is going on: judging by the ball flying through the air, it must be a kaats match.
Kaatsen is a ball sport played on a field measuring 200 by 104 feet. Two teams of three players each alternately try to hit a small leather ball as far as they can with their gloved hand. The exact place where the ball has landed is marked with a small block of wood, called kaats. The opponent must try to hit the ball farther.
Although the game is virtually exclusively played in Friesland now, its origin does not lie there; it was introduced around 1500, by dike workers from Holland.