Wave with one not trying fairground ride? (13)
I believe the answer is:
rollercoaster
'fairground ride?' is the definition.
(I've seen this before)
'wave with one not trying' is the wordplay.
'wave' becomes 'roller' (roller is a kind of wave).
'with' is a charade indicator (letters next to each other).
'one not trying' becomes 'coaster' (to coast is to act lazily or without effort).
'roller'+'coaster'='ROLLERCOASTER'
(Other definitions for rollercoaster that I've seen before include "Fairground ride" , "fairground attraction" , "Big dipper" .)