If you have went to create an event (from the 'Add Events' section and noticed a team name without their division/tier/etc in brackets beside the name, this is a non-league opponent.
Non-league opponents are usually created during an event import, or they can be created manually.
To add or edit a non-league opponent:
1. Go to Schedule / Scores and click 'Scheduled Events'
2. Click 'Non-League Opponents'
You can then add a new opponent or edit/delete an existing non-league opponent.