Sneer at a good fellow (5)
I believe the answer is:
scout
'sneer at' is the definition.
(thesaurus)
'a good fellow' is the wordplay.
I cannot really understand how this works, but
'fellow' could be 'co' (eg a co-worker is a fellow worker) and 'co' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for scout that I've seen before include "One searches for and recruits talented people" , "Talent seeker - boy on a jamboree" , "Reconnoitre" , "Soldier on a reconnaissance mission" , "Soldier on a recce mission" .)