If you wanted to set up a trigger campaign, the trigger could be:
Score is Changed: [specify score field]
(add constraint) New Score is Less Than 0
- or -
Data Value Changes: [specify attribute name]
(add constraint) New Value is Less Than 0
For a batch campaign, the filter could be:
Score was Changed: [specify score field]
(add constraint) New Score is Less Than 0
- or -
[specific field] Score: is Less Than 0
The flow for both the trigger and batch campaigns would be the same:
Change Data Value:
Attribute: [specify score field]
New Value = 0
Setting up your campaign like this will cause any score changes below 0 to either trigger, or be addressed by a batch campaign, and the score field to be reset to zero.