Police pick people out of the crowd, then rush forward. Frightening.
this is a common police tactic. They are called extraction teams
a commanding officer will make the decision and then an extraction team will form behind the riot cop line. The lead officer in the team will tap the shoulder of the riot police and the line will open up to let the team rush forward. Often they will move in a diamond formation with the officers responsible for arresting in the middle surrounded by 4-6 cops protecting them. If you see this happening they are trying to get somebody. Stay on your toes and keep eachother safe!