Show son must be trapped in a racket (7)
I believe the answer is:
aladdin
'show' is the definition.
(traditional pantomime)
'son must be trapped in a racket' is the wordplay.
'son' becomes 'lad' (I've seen this before).
'must be trapped in' indicates putting letters inside.
'racket' becomes 'din' (I've seen this before).
'a'+'din'='adin'
'lad' placed inside 'adin' is 'ALADDIN'.
(Other definitions for aladdin that I've seen before include "Pantomime boy with wonderful lamp" , "Light rubber" , "In the Arabian Nights, he acquires a magic lamp" , "A 13 Down" , "Magic lamp man" .)