Sporty cyclist's end in ethical upset (8)
I believe the answer is:
'sporty' is the definition.
(I've seen this before)
'cyclist's end in ethical upset' is the wordplay.
'end' indicates one should take the final letters.
'in' indicates putting letters inside.
'upset' is an anagram indicator.
The final letter of 'cyclist' is 't'.
'ethical' anagrammed gives 'athleic'.
't' put within 'athleic' is 'ATHLETIC'.
(Other definitions for athletic that I've seen before include "Good at running and jumping" , "Lithe cat (anag.)" , "Active and fit for sport etc" , "Muscular" , "Physically fit, strong and active" .)