He was outside the house, and he was attracting a crowd, hurling incendiary comments at the cop. That’s creating a clear and present danger for the officer.
That is absolute bull. Crowley never even slightly implies that he was afraid of any unruly behavior from the onlookers. In fact, he explicitly says that police and citizens alike appeared "surprised and alarmed" at Gates' words.
You could use the same claim to shut down criticism of ANY gov't official.