Again tried to pass weapon back (5)
I believe the answer is:
resat
'again tried to pass' is the definition.
(sat an exam again)
'weapon back' is the wordplay.
'weapon' becomes 'taser' (taser is a type of weapon).
'back' is a reversal indicator.
'taser' written backwards gives 'RESAT'.
(Other definitions for resat that I've seen before include "did test again" , "Took another chance to pass" , "went back to the paper" , "Tried to pass again" , "was tested again" .)