Blindly attempting to back up and create distance from an armed attacker can create a situation where you will back into or over something that can cause you to lose your balance and give the attacker an advantage.

While I respect this detective not wanting to fire upon this knife-armed suspect advancing upon him, he should have fired a controlled pair to the suspect’s chest when he began advancing. He waited until after he fell and had no chance of escape, and could have easily been killed in the process.