Coach ticket leads to unexpected trouble and strain (4,1,3)
I believe the answer is:
bust a gut
'strain' is the definition.
(I've seen this before)
'coach ticket leads to unexpected trouble' is the wordplay.
'coach' becomes 'bus' (synonyms).
'ticket' becomes 'tag' (I've seen this before).
'leads to' means one lot of letters go next to another.
'unexpected trouble' becomes 'ut' (this could be a standard abbreviation of which I'm unaware).
'bus'+'tag'+'ut'='BUST A GUT'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for bust a gut that I've seen before include "meet qualification for intestinal surgery?" , "Give it everything" , "Really work extra hard" , "Work extra hard to achieve something" , "Make a huge effort (slang)" .)