Troublemaker at start of exclusive social event is a hindrance (9)

'a hindrance' is the definition.
(thesaurus)

'troublemaker at start of exclusive social event' is the wordplay.
'troublemaker' becomes 'imp' (I've seen this before).
'at start of' indicates taking the first letters (I've seen 'at start' mean this).
'social event' becomes 'dance' (I've seen this before).
The first letter of 'exclusive' is 'e'.
'imp'+'e'+'dance'='IMPEDANCE'

'is' acts as a link.