Rotten time handling disarray, not following party line (3-7)

'not following party line' is the definition.
(being off-message is not following an agreed line)

'rotten time handling disarray' is the wordplay.
'rotten' becomes 'off' (rotten food is 'off').
'time' becomes 'age' (an age is a period of time).
'handling' means one lot of letters goes inside another.
'disarray' becomes 'mess' (something in disarray is in a mess).
'off'+'age'='offage'
'offage' enclosing 'mess' is 'OFF-MESSAGE'.