Crossword Genius

Protected oneself and obtained revenge (3,4,3,4)

Ross

I believe the answer is:

got ones own back

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

'protected oneself' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'and obtained revenge' is the wordplay.
I cannot really understand how this works, but
'and' could be 'n' (common abbreviation for 'and') and 'n' is located in the answer.
'obtained' could be 'got' ('get' can be a synonym of 'obtain') and 'got' is located in the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

I've seen this clue in The Irish Times.
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