From Polygon, a gaming website that also does movie reviews:
If you don't have your finger on the trigger and you jump or tense up, nothing happens. If you keep your finger on the trigger when you're not ready to wreck some shit, you may end up accidentally wrecking some shit
http://www.polygon.com/2016/9/22/13015516/john-wick-2-poster-trigger-discipline
Police are escalating to drawn guns too early, and putting their finger on the trigger before they see an actual firearm in the suspect's hand.
If the suspect's hands are in the air, the policeman's finger should be off the trigger.
