In this first sentence, we have a clear case of subject followed by predicate without any elements in between them that would require commas or any other punctuation mark. In the second sentence, the comma between the subject clause "Why Eric dropped the ball" and the predicate "is anyone's guess" should not be there. In the third sentence, a comma must be added after "When the bell rings," since this is an adverbial clause at initial position, which are always followed by a comma.
