Scare ringleader in contest (6)
I believe the answer is:
fright
'scare' is the definition.
(I know that scare can be written as fright)
'ringleader in contest' is the wordplay.
'ringleader' becomes 'r' (first letter of ring).
'in' indicates putting letters inside.
'contest' becomes 'fight' (I've seen this before).
'r' inserted into 'fight' is 'FRIGHT'.
(Other definitions for fright that I've seen before include "Horror" , "Grotesque" , "Terror" , "A scare or shock" , "Panic" .)