The Russian commander's given the push (7)
I believe the answer is:
cossack
'the russian' is the definition.
(I've seen this before)
'commander's given the push' is the wordplay.
'commander's' becomes 'co's' (commanding officer).
'given the push' becomes 'sack' (I can't justify this - if you can you should give a lot more credence to this answer).
'cos'+'sack'='COSSACK'
Can you help me to learn more?
(Other definitions for cossack that I've seen before include "Member of Russian, Ukrainian people" , "One of a people from SW Russia, Ukraine" , "One from southern Russia or Ukraine noted for horse riding skills" , "Belligerent Russian" , "One of an elite cavalry corps in tzarist Russia" .)