"You don't have to retreat, but you do have to move your feet."- 21 foot rule guy on how police can deal with knives without dying and without necessarily shooting someone.
Among reforms discussed at length were retraining all officers in deescalation tactics and abandoning training that teaches the “21-foot-rule” — a turn of phrase taught to nearly all current U.S. police officers that is often interpreted by officers to mean they are justified in shooting any suspect with a knife or edged weapon who comes within 21 feet of them.
Read More: https://www.washingtonpost.com/news/post-nation/wp/2016/01/29/police-chiefs-consider-dramatic-reforms-to-officer-tactics-training-to-prevent-so-many-shootings/