Angry purist locks door at foundation or enters forcibly? (7)

I believe the answer is:

irrupts

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'enters forcibly?' is the definition.
(I've seen this before)

I don't understand the rest of the clue.

(Other definitions for irrupts that I've seen before include "Stirrup? (anag)" , "Breaks in" , "Makes a sudden entry or invasion" , "Bursts into, enters forcibly" .)

I've seen this clue in the Irish Times (Crosaire) and the Irish Times.

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