I don't know what a US cop looks like on an ordinary day, but that group look like they are expecting trouble. There might be riots or unrest in their recent history. If you approach a group like that, things might happen that you don't deserve.
> Think about your grandpa, imagine if he was the one pushed to the ground and now in ICU and tell me again how stressful it must be to stand in full riot gear and have him approach you, alone.
Police aren't lab technicians, they work in an environment where they routinely have to deal with violent criminals who have no respect for the law.
It would remain a stressful job, even if I don't like the police.
And they should have been stressed; they did the wrong thing and are now in a lot of trouble. If anything, they should have been more stressed.
This is exactly what the protestors are saying about the police treatment of black people.