Strike King, finally showing sharpness (4)
I believe the answer is:
tang
'sharpness' is the definition.
(I've seen this before)
'strike king finally' is the wordplay.
'strike' becomes 'tan' (both can mean to hit).
'finally' suggests the final letters.
The final letter of 'king' is 'g'.
'tan'+'g'='TANG'
'showing' is the link.
(Other definitions for tang that I've seen before include "Bite" , "Tart spiciness" , "Strong taste; Chinese dynasty" , "Strong taste or smell" , "Strong flavour" .)