From the "Preferences" panel, under "Report Popup Menu Options", you will need to modify the "Filter" option under the "Game (Boxscore) Type column. The default is "<none>" which shows boxscores for all games. To allow for only League and Post-season game types, select:
WHERE GameType = 'League' OR GameType = 'Post-Season'
To allow for a custom Game Type, you can type in the combination box something like:
WHERE GameType = 'League' OR GameType = 'Tournament'