Supports best Brexit safety feature (8)

I believe the answer is:

backstop

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

'brexit safety feature' is the definition.
I can't judge whether this defines the answer.

'supports best' is the wordplay.
'supports' becomes 'backs' (backing is a kind of supporting).
'best' becomes 'top' (associated in meaning).
'backs'+'top'='BACKSTOP'

Can you help me to learn more?

(Other definitions for backstop that I've seen before include "baseball player" , "baseball catcher" .)

I've seen this clue in The Sun.

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