Fake coach has to go back (5)
I believe the answer is:
bogus
'fake' is the definition.
(I know that fake can be written as bogus)
'coach has to go back' is the wordplay.
'coach' becomes 'bus' (synonyms).
'has' is an insertion indicator.
'to go back' becomes 'og' (I can't justify this - if you can you should give a lot more credence to this answer).
'bus' placed around 'og' is 'BOGUS'.
Can you help me to learn more?
(Other definitions for bogus that I've seen before include "Pretended" , "Spurious" , "Mock" , "that's not real" , "Fictitious" .)