An example would be any case in which a weapon was used--a knife or a firearm. Often if a firearm is involved, it may be a more serious offence, but a knife might be a common weapon used in those kinds of assaults that actually cause the officer some significant bodily harm. Common assault involves a very wide range of things that constitute an assault on the officer, but when they actually cause any significant bodily harm, if someone uses a weapon, that would be a more serious offence. It would be an even more serious offence if they wounded, maimed, disfigured, or endangered life. Those cases would constitute an aggravated assault, and that's the most serious level of assault.
