The most important attribute of a ball player, is quick reflex actions. We laid out our music and snacks, and began to study. I turned the corner, and ran smack into a patrol car. She was late for class, because her alarm clock was broken. You ought to see a doctor, if you are ill.
Commas help the reader to see the necessary separation between ideas within the sentence.
The game was over, but the crowd refused to leave. DO use commas after introductory clauses, phrases, or words that come before the main clause. Because her alarm clock was broken, she was late for class. If you are ill, you ought to see a doctor. DO use a pair of commas in the middle of the sentence to set off phrases, clauses, and words which are NOT essential to the meaning of the sentence.