Nonsense about coach being tough (6)
I believe the answer is:
robust
'tough' is the definition.
(thesaurus)
'nonsense about coach' is the wordplay.
'nonsense' becomes 'rot' (I've seen this before).
'about' is an insertion indicator.
'coach' becomes 'bus' ('bus' can be a synonym of 'coach').
'rot' going around 'bus' is 'ROBUST'.
'being' is the link.
(Other definitions for robust that I've seen before include "Vigorous - healthy" , "Study and durable" , "Strong and healthy" , "Turbos (anag) - fit for purpose!" , "Rugged and sturdy" .)