That handcuffing permits police to turn their backs and proceed to investigate other people. They were detained, not arrested. It is standard procedure and one you would use if you were outnumbered and needed to protect not only yourself but all the other people involved. It is reasonable and not excessive, given the circumstances.
I disagree. Being restrained like a goddamn animal in a potentially chaotic situation like that leaves a person virtually defenseless.
It's tyrannical, plain and simple.
Anybody who is not under arrest should not be handcuffed.