Spear carrier starts to tire, resourcefully flipping axe around (5)
I believe the answer is:
extra
'spear carrier' is the definition.
('extra' can be a synonym of 'spear carrier')
'starts to tire resourcefully flipping axe around' is the wordplay.
'starts to' says to take the initial letters.
'flipping' shows that the letters should be reversed in order.
'around' is an insertion indicator.
The first letters of 'tire resourcefully' is 'tr'.
'axe' backwards is 'exa'.
'tr' going into 'exa' is 'EXTRA'.
(Other definitions for extra that I've seen before include "Another" , "Ancillary" , "someone acting in a crowd" , "entry on scorecard?" , "Surcharge" .)