Not fully in form, Paul gets out and it hurts! (7)

I believe the answer is:

painful

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'not fully in' is the definition.
Both the definition and answer are adjectives. Perhaps they are linked in a way I don't understand?

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for painful that I've seen before include "Agonising" , "Causing trouble or difficulty - it hurts" , "Distressing or hurtful" , "Tender" , "Inflamed" .)

I've seen this clue in the Evening Standard.

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