An eccentric, but a first-class shot (8)
I believe the answer is:
crackpot
'an eccentric' is the definition.
(I know that crackpot is a type of eccentric)
'a first-class shot' is the wordplay.
I cannot quite understand how this works, but
'a' is present in the answer.
'first-class' could be 'c' (1st letter of 'class') and 'c' is present in the answer.
This explanation may well be incorrect...
'but' is the link.
Can you help me to learn more?
(Other definitions for crackpot that I've seen before include "Nut" , "Eccentric (colloq.)" , "Nutty" , "Idiot" , "Informal eccentric like damaged utensil" .)