Lawsuit basis (4)
I believe the answer is:
tort
'lawsuit basis' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tort that I've seen before include "Civil wrong or injury" , "Small tropical fish" , "Wrongdoing for which damages may be sought" , "A legal wrong open to claim for damages" , "Legal wrongdoing" .)