Leaves rich gallants to go astray (10)

I believe the answer is:

chevaliers

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'gallants to go astray' is the definition.
I can't tell whether this defines the answer.

'leaves rich' is the wordplay.
'leaves rich' anagrams to 'CHEVALIERS'.
Though, I am not clear how this is indicated.

Can you help me to learn more?

I've seen this clue in The Irish Independent.

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