This is the simplest way to deal with scoring one team. Presuming you want to at least know the totals for your opponent at each period.
From the game scoring page.
Touch the score in the scoreboard for the team you just want to enter totals for (the opponent) in this example that is the Guest team.
A scoring page will appear.
Simple adjust the score to reflect the total at the end of each period.
Note that by doing this you will be unable to determine some statistics which require data from the opponent.