Frustrated at fencing? (6)

I believe the answer is:

foiled

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'frustrated' is the definition.
(I know that frustrated can be written as foiled)

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for foiled that I've seen before include "Thwarted with sword?" , "Thwarted, frustrated" , "Thwarted, defeated" , "Prevented the success of" .)

I've seen this clue in the Evening Standard.

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