Club to move against being infiltrated by left (8)
I believe the answer is:
bludgeon
'club' is the definition.
(bludgeon is a kind of club)
'move against being infiltrated by left' is the wordplay.
'move' becomes 'budge' (budging is a kind of moving).
'against' becomes 'on' (I've seen this in other clues**).
'being infiltrated by' indicates putting letters inside.
'left' becomes 'l' (common abbreviation).
'budge'+'on'='budgeon'
'budgeon' placed around 'l' is 'BLUDGEON'.
'to' is the link.
(Other definitions for bludgeon that I've seen before include "Short stick with thickened end as weapon" , "Bully; heavy weapon" , "Strike with a club" , "Thick stick with a heavy end" , "Thick stick as weapon" .)