Show friend holding in energy (7)
I believe the answer is:
matinee
'show' is the definition.
(I know that matinee is a type of representation)
'friend holding in energy' is the wordplay.
'friend' becomes 'mate' (mate is a kind of friend).
'holding' is an insertion indicator.
'energy' becomes 'e' (physics symbol as in E=mc2).
'mate' enclosing 'in' is 'matine'.
'matine'+'e'='MATINEE'
(Other definitions for matinee that I've seen before include "Afternoon show" , "Daytime performance of play etc" , "First jackets" , "After lunch, show" , "Afternoon performance (of play etc)" .)