Sudden energy after I am timed swimming (9)
I believe the answer is:
immediate
'sudden' is the definition.
(thesaurus)
'energy after i am timed swimming' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mc2).
'after' is a charade indicator (letters next to each other).
'swimming' is an anagram indicator.
'am'+'timed'='amtimed'
'amtimed' anagrammed gives 'mmediat'.
'i'+'mmediat'='immediat'
'e' after 'immediat' is 'IMMEDIATE'.
(Other definitions for immediate that I've seen before include "Instantaneous" , "Involving no delay" , "Nearest" , "Direct" , "Prompt,straightaway" .)