Crossword Genius

Travelling crowd celebrate on top of train? Quite the opposite (5,5)

Ross

I believe the answer is:

coach party

I'm a little stuck... Click here to teach me more about this clue!

'top of train? quite the opposite' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.

'travelling crowd celebrate on' is the wordplay.
'travelling crowd' becomes 'coach' (I can't justify this - if you can you should give a lot more credence to this answer).
'celebrate' becomes 'party' (partying is a kind of celebrating).
'on' is a charade indicator (letters next to each other).
'coach'+'party'='COACH PARTY'

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