Fit to dispute losing right (4)
I believe the answer is:
ague
'fit' is the definition.
(I've seen this before)
'dispute losing right' is the wordplay.
'dispute' becomes 'argue' (to argue something is to dispute or contest it).
'losing' is a deletion indicator.
'right' becomes 'R' (common abbreviation).
'argue' with 'r' removed is 'AGUE'.
'to' acts as a link.
(Other definitions for ague that I've seen before include "Fever with shivers" , "nasty illness?" , "Feverish fit" , "met with cheek in Twelfth Night" , "Old word for fever" .)