Fish food with crust son Charlie tucks into (6)
I believe the answer is:
pisces
'fish' is the definition.
(I've seen this before)
'food with crust son charlie tucks into' is the wordplay.
'food with crust' becomes 'pies'.
'son' becomes 's'.
'charlie' becomes 'c' (phonetic alphabet: alpha, bravo, charlie etc.).
'tucks into' is an insertion indicator.
's'+'c'='sc'
'pies' going around 'sc' is 'PISCES'.
(Other definitions for pisces that I've seen before include "Spice for the Fish" , "Twelfth zodiacal sign" , "Fish star sign" , "The twelfth sign of the zodiac, the fishes" , "'Sign of the zodiac, the fish (6)'" .)