American 'no' upset king (4)
I believe the answer is:
yank
'american' is the definition.
(Yank is an example)
'no upset king' is the wordplay.
'no' becomes 'nay' (I've seen this before).
'upset' is a reversal indicator.
'king' becomes 'k'.
'nay' written backwards gives 'yan'.
'yan'+'k'='YANK'
(Other definitions for yank that I've seen before include "Tug shaply" , "Big jerk!" , "one seen crossing the Atlantic?" , "Pull with a sudden movement" , "Term for an American" .)