Q: Is there a way to mark a forfeit?
Yes, you can mark a game as a forfeit via the edit game dialog.
In your standings configuration, you can also set a number of points to be subtracted for a forfeit or awarded for a win by forfeit (given your standings use points, e.g. 3 points for a win).
What if both teams forfeit?
Another way to deal with forfeits, particularly when both teams do, would be to add a team named Forfeit and put it in its own division, then remove that division from your season so that it doesn't show in standings.
Then you can click the edit button on the game to swap in the Forfeit team (and click Add A Game to add the forfeit for the opponent).
Now you can enter a score that just gives the forfeiting team a loss.
If you're on LITE, you don't have divisions, so you would
add the team via the Teams button on your schedule maker, then
add the games via the Add a Game button, then
delete the team via the Teams button (don't delete the games when asked)