Club's record number of points at start of season (5)
I believe the answer is:
disco
'club's' is the definition.
(I've seen this before)
'record number of points at start of season' is the wordplay.
'record' becomes 'disc' (synonyms).
'number of points at start of season' becomes 'O' (O resembles 0).
'disc'+'o'='DISCO'
(Other definitions for disco that I've seen before include "'Genre of dance music, popular in the 1970s (5)'" , "Musical party" , "Dance party" , "lively entertainment, for some?" , "Youngsters' dance venue" .)