Mock old fool forgetting street (4)

I believe the answer is:

jeer

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'mock' is the definition.
(I know that jeer is a type of rally)

I don't understand the rest of the clue.

(Other definitions for jeer that I've seen before include "Rudely mocking remark" , "Catcall" , "Taunt" , "Henry ---, Richard II's enemy, successor" , "Mock publicly" .)

I've seen this clue in The Daily Mail.

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