King and others worried about current counterattack (9)
I believe the answer is:
retaliate
'counterattack' is the definition.
(I know that counterattack is a more specific form of the action retaliate)
'king and others worried about current' is the wordplay.
'king' becomes 'R' (abbreviation for rex, king in Latin).
'and others' becomes 'etal' (short for 'et alia', 'and others' in Latin).
'worried' becomes 'ate' (something worrying may eat someone up).
'about' means one lot of letters go next to another.
'current' becomes 'I' (symbol for electric current).
'ate' put after 'i' is 'iate'.
'r'+'etal'+'iate'='RETALIATE'
(Other definitions for retaliate that I've seen before include "Repay injury with similar one" , "settle accounts" , "Make tit-for-tat attack" , "reply" , "Strike back, avenge" .)