Lose track? (6)
I believe the answer is:
derail
'lose track?' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for derail that I've seen before include "Of train, force off tracks" , "create an obstructive diversion" , "Cause to run off the tracks" , "put off track" , "get off the line" .)