First and foremost, shooting is incorrectly viewed by many as a legitimate dispute resolution mechanism. Nonexistent training on how to keep interactions from escalating coupled with a glaring absence of non-lethal options all but ensures a shooting at the instant a cop feels he is in a situation that he can no longer control, either due to noncompliance or when within a crowd of people that is closing in.
In the video, the number of people who are still within a threatening distance of the cop after the shot was fired and the number of those bystanders who proceeded to run around in anger were just tempting fate. Luckily nothing else happened. Shooting someone in the foot, is a novel approach through. I wonder if as is usually the case this cop was aiming somewhere else (like the sand) and ended up actually hitting a person. It might be possible this cop only intended a show of force but because he put his finger on the trigger, he was but a twitch and a 1/2 inch away from firing.
Cops are unpredictable here, one needs to be careful around them even if you are not directly involved in an interaction. They can go from apathetic to full on cowboy really quickly and they are terrible shots at anything more than 10 feet away. By enlarge they don't aim and have no idea what a correct sight picture looks like.