Crossword Genius

Pins an opponent's arms, making him defenceless? (6,3,4)

Ross

I believe the answer is:

spikes his guns

I'm a little stuck... Click here to teach me more about this clue!

'pins an opponent's' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.

'arms making him defenceless?' is the wordplay.
I cannot really see how this works, but
'arms' could be 'pikes' (pike is a kind of arm) and 'pikes' is present in the answer.
'him' could be 'gun' and 'gun' is found within the answer.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Globe and Mail.
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