Spoil those attending resort (7)
I believe the answer is:
margate
'resort' is the definition.
(I have seen 'coastal resort' mean 'margate' so perhaps 'resort' could also mean 'margate')
'spoil those attending' is the wordplay.
'spoil' becomes 'mar' (synonyms).
'those attending' becomes 'gate' (the number of people attending a sporting event).
'mar'+'gate'='MARGATE'
(Other definitions for margate that I've seen before include "which people may visit for seaside holiday" , "resort town" , "place in England" , "coastal resort" , "N. Kent seaside resort" .)