That was a joke. Let me tell you the reason why it is funny...
I was wondering why the ball kept getting bigger and bigger
I was wondering why the ball kept getting bigger and bigger, and then it hit me.
This is a pun. The critical element of the joke is the ambiguity of the sentence. Either the "then it hit me" means that the ball hit the jokester, or the solution to the question of why the ball kept getting bigger hit the jokester.