Composer about to back away from gun carrier? (5)

I believe the answer is:

holst

'composer' is the definition.
(Gustav Holst)

I cannot understand how the rest of the clue works.

(Other definitions for holst that I've seen before include "Gustav --, English composer" , "British composer, 1874-1934" , "Gustav - (The Planets)" , "Composer of The Planets, d. 1934" , "Planets Suite composer" .)

I've seen this clue in The Guardian.

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