If Nick throws first of stones then duck! (4)
I believe the answer is:
teal
'duck' is the definition.
(teal is a type of duck)
'if nick throws first of stones' is the wordplay.
I cannot really see how this works, but
'first' could be 'a' (first letter of the alphabet) and 'a' is found in the answer.
The remaining letters 'tel' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'then' acts as a link.
Can you help me to learn more?
(Other definitions for teal that I've seen before include "Variety of small ducks" , "Duck; greenish-blue colour" , "Strange tale of a duck" , "Duck - dark greenish-blue" , "Variety of duck" .)