He could see how angry and frustrated his son was by how hard he was throwing the ball. In this case, the child seemed to be using the game as a way to release a pile of hurt feelings that had nothing to do with baseball. Not every game of catch, or every playtime with a child, contains all of these multiple levels of meaning. But above and beyond simple playfulness, all play is more profoundly meaningful than we usually think. Like lion cubs wrestling each other, play is a way to try on adult roles and skills.
Human children roughhouse, and they play house.
As children discover the world, and discover what they are able to do in the world, they develop confidence and mastery. Play is also a way to be close, and even more importantly, a way to reconnect after closeness has been severed. Chimpanzees like to tickle each others palms, especially after they have had a fight. The third purpose of play for children, and perhaps the one that is most uniquely human, is to recover from emotional distresses. Imagine your child has had a hard day at school.