Delayed - and real energy lost by the side (7)
I believe the answer is:
lateral
'the side' is the definition.
(thesaurus)
'delayed and real energy lost' is the wordplay.
'delayed' becomes 'late' (I've seen this before).
'and' is a charade indicator (letters next to each other).
'energy' becomes 'e' (physics symbol as in E=mc2).
'lost' is a deletion indicator.
'real' with 'e' taken away is 'ral'.
'late'+'ral'='LATERAL'
'by' acts as a link.
(Other definitions for lateral that I've seen before include "Relating to the side" , "Tall ear (anag.)" , "Sort of thinking" , "Sideways, like creative thinking" , "belonging to the side" .)