One must play by the rules, otherwise you can not play tennis. Most rules are obvious but some are a little difficult. Strange things can happen on the court which can easily lead to disagreement. Who is actually right? Here you can find all the rules (PDF file). It is also possible to search the text. Click “Ctrl F” and a box opens that says search.
Example: Is it the opponent’s score if you hit the ball twice in the same swing?
ANSWER: No, it only counts as one stroke and the game continues until someone wins the point.