I designed and built a website for one of my sports leagues. I thought I had everything covered until there was a forfeit. Since I also built a CMS for the site to be managed by the league operators, they just made the score 1-0. The challenges posed by a forfeit is that there is not a score, but it is counted as a win for the team that didn't forfeit. One idea I have is to add an asterisk to the losing score indicating a forfeit that the content editor can toggle, but as the infomercial phrase goes, "There's got to be a better way!".
How to score a forfeit
Rules vary on how to score a forfeit, I would look up the rules for your specific case. E.g. for FIFA it is 3-0 (if the score from the winning team isn't higher) (see wikipedia on forfeit).
How to display a forfeit
I would display both the score and a label with forfeit. I think forfeit should be more prominent because the score is artificial in that case. Something like the example below.