D was on a bus when he saw what he thought was a man assault a youth but it was actually a police officer trying to arrest the youth for mugging an old lady. V didn't show his badge and therefore was an altercation where the officer was injured. The courts quashed the conviction because the jury should have been told the if D thought the mistake was genuine they should judge the D according to his genuine view of the facts, whether this mistake was reasonable or not. S.76(3) and (4) states the D is to be judged in the facts they believed them to be, giving this case a statutory footing.