Beatles' final pathetic track (5)
I believe the answer is:
spoor
'track' is the definition.
(spoor is a kind of track)
'beatles' final pathetic' is the wordplay.
'final' says to take the final letters.
'pathetic' becomes 'poor' ('poor' can be a synonym of 'pathetic').
The last letter of 'beatles' is 's'.
's'+'poor'='SPOOR'
(Other definitions for spoor that I've seen before include "Beast's trail" , "Track of wild animal" , "Animal track or scent" , "Animal's track/scent" , "Animal's track or scent" .)