Club record set to be broken by United (6)
I believe the answer is:
cudgel
'club' is the definition.
(I know that cudgel is a type of club)
'record set to be broken by united' is the wordplay.
'record' becomes 'CD' (compact disc).
'set' becomes 'gel' (both can mean to harden).
'to be broken by' indicates putting letters inside (inserted letters break into the word).
'united' becomes 'U' (as in Man U, Manchester United).
'cd'+'gel'='cdgel'
'cdgel' enclosing 'u' is 'CUDGEL'.
(Other definitions for cudgel that I've seen before include "Blunt instrument" , "Short stout stick" , "Short thick stick used as weapon" , "Wooden weapon" , "brain" .)