There is likely no need for a waiver in situations where implied consent exists. Implied consent exists when there are known risks.
For example, in sporting events, there is implied consent for ordinary risks. In Elliott and Elliot v. Amphitheatre Ltd. [1934] M.J. No. 19, a hockey fan was hit with a puck. The court found that because the plaintiff was an amateur hockey player, he was aware of the risks.
This known risk resulted in implied consent to the ordinary risks associated with attending a hockey game. Implied consent, however, is exceeded in cases where injury goes beyond the scope of the implied consent. For example, in Agar v. Canning 54 W.W.R. 302, the plaintiff attempted to delay the defendant during a hockey game by hooking him with his stick and administering a painful blow to the back of the neck. In retaliation, the defendant used his stick to hit the plaintiff in the face, between the nose and the right eye. The plaintiff suffered unconsciousness and loss of vision in right eye. The court held that injuries were inflicted under circumstances which show a definite resolve to cause serious injury to another.
Even when there is a provocation, these actions do not fall within the scope of the implied consent.
See also: Wright v. McLean 20 W.W.R. 305, where four boys were playing near a mound of dirt and throwing mud at each other. The defendant was riding his bike and was struck. The defendant was invited to join the play. The boys kept throwing mud balls at each other. The defendant struck the plaintiff accidentally in the face with a rock. Plaintiff sued in battery. The court held that act was unintentional and that in joining the game the plaintiff implied consent to risks associated with the game.