Collapsed on tenth lap in this challenge (10)
I believe the answer is:
pentathlon
'challenge' is the definition.
(I know that pentathlon is a type of challenge)
'collapsed on tenth lap' is the wordplay.
'collapsed' indicates anagramming the letters.
'on'+'tenth'+'lap'='ontenthlap'
'ontenthlap' anagrammed gives 'PENTATHLON'.
'in this' acts as a link.
(Other definitions for pentathlon that I've seen before include "sports event" , "Event of five different disciplines" , "Fivefold athletic event" , "Sporting event with five disciplines" , "old Olympic event" .)