Sea mammal overturned small egg at afternoon performance (7)
I believe the answer is:
matinee
'afternoon performance' is the definition.
(I've seen this in another clue)
'sea mammal overturned small egg at' is the wordplay.
I cannot quite understand how this works, but
'at' could be 'in' and 'in' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for matinee that I've seen before include "sort of jacket" , "Afternoon performance (of play etc)" , "theatre performance" , "Afternoon show" , "in which players may appear?" .)