A target on the green flag (4)

I believe the answer is:

jack

I believe this is a double definition.

'a target on the green' is the first definition.
(target on a bowls green)

'flag' is the second definition.
(I know that jack is a type of flag)

(Other definitions for jack that I've seen before include "Target ball in bowls" , "Sort of boot, hammer, pot or tar" , "PANTO (part title)" , "Sailor; flag" , "bowler rolls it" .)

I've seen this clue in The Guardian.

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