Trail bikes at the back broke (5)
I believe the answer is:
spoor
'trail' is the definition.
(I've seen this before)
'bikes at the back broke' is the wordplay.
'at the back' says to take the final letters.
'broke' becomes 'poor' ('poor' can be similar in meaning to 'broke').
The final letter of 'bikes' is 's'.
's'+'poor'='SPOOR'
(Other definitions for spoor that I've seen before include "Animal's track or scent" , "Track of wild animal" , "Animal track or scent" , "Beast's trail" , "Animal's track/scent" .)