At one point in time the law seemed clear that consent could not be a defence to an assault charge that aroes out of a fist fight where injury resulted. The courts said there was little value in encouraging post bar brawls by allowing such a defence. But over the last number of years that position has changed. In some cases, even with more serious offences, the defence has been succesful.
In R. v. McDonald, the Ontario Court of Appeal clarified that the defence is available even in the case of aggravated assault. It does not apply only in a situation where when the accused intended to cause serious bodily harm and the accused caused serious bodily harm. In other words, even in cases where serious bodily harm occurs, the defence is still available if the accused did not intend to cause that serious bodily harm. For instance, a single punch might cause serious injuries when an individual falls to the ground and hits his head. If the accused did not intend this harm to occur then the defence of consent could potentially be succesful.
As a result of this case, and a number of others that have followed it, the defence of consent is potentially available in fight scenarios for offences such as assault, assault causing bodily harm, assault with a weapon, aggravated assault, and even manslaughter.