The fact that Fien is (a) small, and (b) a half-back, is entirely irrelevant.
While I don't condone king-hits, I also don't see how Ricketson had "no business" in that altercation. FFS, he was standing right there! Was he supposed to stand back and start cheering them on? Fact is, once a blue starts of the field, every player is entitled to come in and do his bit. Ricketson should probably have been separating the players/pushing Fien out of the way instead of hitting him, but then again, plenty of players have come in swinging in the past and been applauded for "sticking up for their teammates", "going the biff" etc. I also find the definition of a king-hit/cheap shot to be very contentious. Tell me, why do players throw punches at each other? Do they want to miss? Should Ricketson have tapped Fien on the shoulder and told him "I'm going to hit you now", just so it didn't hurt him too much?