Fight and thrash a tough character (7)
I believe the answer is:
spartan
'a tough character' is the definition.
(as in a Spartan warrior)
'fight and thrash' is the wordplay.
'fight' becomes 'spar' (sparring is a kind of fighting).
'and' says to put letters next to each other.
'thrash' becomes 'tan' (I've seen this in another clue).
'spar'+'tan'='SPARTAN'
(Other definitions for spartan that I've seen before include "Indifferent to luxury" , "Ascetic - ancient Greek" , "toughly-disciplined type" , "Austere - disciplined" , "Disciplined person" .)