The insouciant way in which Algy gets out of line (5)

I believe the answer is:

gaily

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'out of line' is the definition.
Both the definition and answer are adverbs. Maybe you can see a link between them that I can't see?

I don't understand the remainder of the clue.

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(Other definitions for gaily that I've seen before include "Cheerily, brightly" , "In merry or light-hearted manner" , "Merrily" , "Light-heartedly" .)

I've seen this clue in the Evening Standard.

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