A "shame" factor could be added for each player. If a higher level player tries to kill a newbie (and I mean a guy with level 255 trying to kill a level 1 guy), a dice is throwed and the level 1 guy could kill the 255 guy with one hit
In the other hand, if a level 1 guy tries to kill a 255 guy, this feature is disabled, so newbie backstabing is not allowed
A very good feature and not used in MANY games was included in Diablo. If you keep killing all creatures in the 1rst dungeon level, and restarting the game, you could'nt rise up after level 11 (exp). The exp you gain per killing becomes smaller as your level keeps going up.
It's a very good way to discourage newbie killing, as the killer would get no advantage and takes the risk of dying with one strike.
The same could be implemented with levels, for exemple, if the attacker has >20 levels above the attacked. He would get no experience and have the risk to die.
So what do you think ?