Nasty turn for a little one! (4)
I believe the answer is:
runt
'little one' is the definition.
(I've seen this in another clue)
'nasty turn' is the wordplay.
'nasty' indicates an anagram (a nasty or wrong spelling).
'turn' is an anagram of 'RUNT'.
'for a' acts as a link.
(Other definitions for runt that I've seen before include "little one" , "Weakest animal in a litter" , "Turn into smallest of the litter" , "stunted figure" , "Littlest oinker" .)