Inadmissible act after sailor's change of direction (5,4)
I believe the answer is:
about turn
'change of direction' is the definition.
(about turn is a kind of change of direction)
'inadmissible act after sailor's' is the wordplay.
'inadmissible' becomes 'out'.
'act' becomes 'turn' (theatre**).
'after' says to put letters next to each other.
'sailor' becomes 'ab' (abbreviation for able seaman).
'out'+'turn'='outturn'
'outturn' put after 'ab' is 'ABOUT-TURN'.
(Other definitions for about turn that I've seen before include "Reversal of direction" , "Pivot 180 degress" , "Total change of policy" , "A complete change of policy" , "order to the troops" .)