Do you have to be ahead by two to win when playing darts?

Some matches are played with the rule that you have to win by at least two legs, especially in the last set when playing sets. For example, if you are playing best of five legs per set and best of five sets, you are tied two sets each, and you are tied in the last set two legs each, the match would not be over after the fifth leg because the winner of the fifth leg would be ahead by only one.

The bottom line is that it all depends on what rules you agree to before you start playing.