Struck in the side with a fish! (7)
I believe the answer is:
whiting
'a fish' is the definition.
(whiting is a kind of fish)
'struck in the side' is the wordplay.
'struck' becomes 'hit'.
'in the' means one lot of letters goes inside another.
'side' becomes 'wing' (I've seen this in other clues).
'hit' going within 'wing' is 'WHITING'.
'with' acts as a link.
(Other definitions for whiting that I've seen before include "Small sea fish or ground chalk for painting" , "Edible marine fish" , "[SOMETHING FISHY]" , "North Atlantic food fish" , "Small fish related to cod" .)