The term "king hit" is well known in rugby league and ice hockey circles. It is, of course, not a practice in rugby union. Today, being "king hit" means to be hit heavily when you are not expecting the blow. You do not often rise quickly after being "king hit".
"The rule of law,"
The National Legal Eagle: Vol. 6
, Article 2.
Available at: http://epublications.bond.edu.au/nle/vol6/iss2/2