I have a child with violent tendencies. He is not bigger than me, stronger than me, or faster than me...YET. But he will be. His father is 6'2 and it looks like he might pass him in height when he's all grown up.
Believe me when I say that we take all reasonable precautions in my home, including locking up the sharps, not letting him be alone with the younger kids, and using every in-home alarm system known to man. And in spite of all our precautions, he can hurt himself if he wants, and he can hurt someone else if he really wants to. He knows how to kick, punch, headbutt, bite, and when all else fails, he will vomit or pee on you, if he doesn't want to be held to be calmed down.
Someday, it is highly likely that he will simply pick up a piece of furniture, use a broken piece of glass as a weapon, or simply pick the lock on the drawer that holds the knives, and there will likely be no other choice but to call the police for emergency help. It is, in fact, what his crisis counselor has suggested, and is part of our family safety plan for when that day comes. Younger kids run outside to the truck, lock themselves in and wait for help or the all clear. Mom calls 9-1-1 for police assistance and ambulance transport to the nearest psych hospital. Luckily that's about 5 minutes away.
Calling the police on your child and putting them in a cell might seem like a craxy, cold-hearted solution. It's not. Sometimes, there is no other solution that will keep everyone in the situation safe.