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' indicates putting letters inside.
'to go back' becomes 'og' (I can't explain this - if you can you should give a lot more credence to this answer).
'bus' going 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" .)