Fish sauce over leafy vegetable (8)
I believe the answer is:
Here is my best explanation:
'fish' is the definition.
(pilchard is a kind of fish)
'sauce over leafy vegetable' is the subsidiary indication.
'sauce' becomes 'lip' (I've seen this in other clues).
'over' says the letters should be written in reverse.
'leafy vegetable' becomes 'chard' (chard is a kind of leafy vegetable).
'lip' reversed gives 'pil'.
(Other definitions for pilchard that I've seen before include "type of fish", "item", "'Small fatty fish, usually canned (8)'", "Small fatty fish, usually tinned", "Item of seafood", "Small marine food fish", "Marine food fish", "Fish of herring family", "Small sea fish related to the herring" and "Edible herring relative".)