As a former cop I can say we trained for knife scenarios. I thug with a knife who is within 15 feet of you can become lethal is a few seconds - especially if that thug is trained with edge weapons and knows how and where to deliver a fatal slash that will cause the LEO to bleed out in two minutes.
Knife in the hands of a thug should always mean drawn weapon in the hands of a cop. NOTHING LESS.
And he can still be lethal even if you put a round in him. The are tons of instances where a perp kept coming even after taking one to the chest. And there are a lot of police training videos on youtube demonstrating that a thug with a knife at 30 feet can close and stab an officer before the officer can unholster and present his weapon. And in those videos the officer knew he was going to be coming.
One pulls out a knife, and starts acting weird. Cops show up, and ask/demand that he drop the knife, telling him "...or they'll shoot him with a pepper ball" and take him into custody.
The bum then decides to start superficial carving a bulls eye on his shirtless chest "to make it easier for the cops to aim" - his words.
Not sure if the cops waited for the knife to be out of the way to loose the pepper ball. Just think of the fuss if the ball had hit the back of the hilt, and helped the knife to penetrate deeper.