What is a ball pit?
a box with balls inside.
A ball pit (originally called “ball crawl” and also known as a ball pool or ball pond) is a padded box or pool filled with small (generally no larger than 2.75 inches (7.0cm) in diameter) colorful hollow plastic balls. Instead of balls, other spherical objects can be used, such as balloons. It is typically employed as a recreation and exercise for children.
a game in which people toss balls in to a large hole in the ground.