“... a tip concerning a large group wearing matching outfits and masks.”
We need to be calling in a lot of tips come Football season.
Antifa members tend to wear all black outfits and wear masks, but I haven’t heard of any pre-assault arrests of them.
The “tip” thing is nonsense - a lie, most likely. That was said by police because they had no actual reasonable expectation they were ‘planning to riot’ other than how they were dressed and riding in the same vehicle. The “tip” gave them the legal basis for further persecution and “found evidence.”
Most of them were sporting identical high and tight haircuts.