Side labour to provide group action (8)
I believe the answer is:
teamwork
'group action' is the definition.
(teamwork is a kind of group action)
'side labour' is the wordplay.
'side' becomes 'team' (a side is a sporting team).
'labour' becomes 'work' (I've seen this before).
'team'+'work'='TEAMWORK'
'to provide' acts as a link.
(Other definitions for teamwork that I've seen before include "Concert" , "Effective action of a group" , "Organised co-operation, group endeavour." , "Co-ordination" , "It demands action by several folk" .)