One might run cycling heat without permit (7)
I believe the answer is:
athlete
'one might run' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'cycling heat without permit' is the wordplay.
'cycling' indicates anagramming the letters.
'without' indicates putting letters inside ('without' can be similar in meaning to 'outside').
'permit' becomes 'let' (synonyms).
'heat' anagrammed gives 'athe'.
'athe' placed around 'let' is 'ATHLETE'.
Can you help me to learn more?
(Other definitions for athlete that I've seen before include "Strangely, the tale of one who is fit" , "Track and field competitor" , "Person trained to compete in sports" , "eg Dean Macey" , "Track eventer" .)