Fight against others, holding one pole (6)
I believe the answer is:
resist
'fight against' is the definition.
(I've seen this in another clue)
'others holding one pole' is the wordplay.
'others' becomes 'rest' (eg the rest of a group).
'holding' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'pole' becomes 's' (abbreviation for South, as in South Pole).
'i'+'s'='is'
'rest' placed around 'is' is 'RESIST'.
(Other definitions for resist that I've seen before include "Put up opposition to sister" , "Use force to prevent something from happening to sister" , "turn down" , "'Withstand, fight against (6)'" , "Withstand or defy" .)