Keep down if soldiers push (7)
I believe the answer is:
repress
'keep down' is the definition.
('repress' can be a synonym of 'keep down')
'soldiers push' is the wordplay.
'soldiers' becomes 're' (Royal Engineers).
'push' becomes 'press' (press is a kind of push**).
're'+'press'='REPRESS'
'if' acts as a link.
(Other definitions for repress that I've seen before include "Check" , "Keep in subjection" , "Forcibly keep down" , "Subdue" , "Restrict freedom of" .)