The thing you don't want to be left in (5)

I believe the answer is:

lurch

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'the thing' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Maybe there's an association between them I don't understand?

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for lurch that I've seen before include "Pitch to one side" , "Abrupt uncontrolled movement - something not to be left in?" , "Faltering movement" , "Stagger; (leave in ) difficulties" , "Totter" .)

I've seen this clue in the Evening Standard.

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