The odd cat loses its tail in a fight (6)
I believe the answer is:
rumpus
'loses its tail in a fight' is the definition.
I can't tell whether this definition defines the answer.
'the odd cat' is the wordplay.
'the odd' becomes 'rum' (rum can mean strange or dubious).
'cat' becomes 'pus' (I can't justify this - if you can you should believe this answer much more).
'rum'+'pus'='RUMPUS'
Can you help me to learn more?
(Other definitions for rumpus that I've seen before include "5a [BALLYHOO] involving noise" , "Uproar or angry dispute" , "'Commotion, din (6)'" , "Kerfuffle" , "To-do" .)