In the course of fights thrash Greeks (8)
I believe the answer is:
spartans
'greeks' is the definition.
(Spartan is an example)
'in the course of fights thrash' is the wordplay.
'in the course of' means one lot of letters goes inside another.
'fights' becomes 'spars' (sparring is a kind of fighting).
'thrash' becomes 'tan' (I've seen this before).
'spars' placed around 'tan' is 'SPARTANS'.
(Other definitions for spartans that I've seen before include "These old Greeks lived frugally and harshly" , "Hardy old Greeks" , "Hardy and frugal citizens of old Greece" , "hardy fellows" , "Harshly treated citizens once" .)