Then you didn't watch the videos in the story Burr linked. They were all covering their ears at least in the second video. The first has been removed by the user on youtube.

It's come out multiple times in the news that a lot of times the anarchists are actually working for the police, so that the state can have an excuse to shut down protests.

Provocateur Cops Caught Disguised As Anarchists At G20 Shocking video has emerged of cops posing as anarchist protesters at the G20 Summit in Pittsburgh, in yet another example of authorities attempting to provoke chaos at global summits in order to justify a brutal police crackdown.Footage from Saturday night shows three burly older men who look completely out of place with black bandanas over their face walking alongside young protesters during a march against police brutality in a You Tube clip entitled “G20 Epic Undercover Police Fail”.The clip would be hilarious if it was not so disturbing. Protesters walking behind what are obviously badly disguised cops claim they broke cameras and acted aggressively towards genuine protesters, as well as carrying gas canisters. During a peaceful demonstration on Saturday night, riot cops savagely attacked protesters with batons and rubber bullets while also assaulting and arresting students who weren’t even part of the demonstration.[youtube]<object width="560" height="340"><param name="movie" value="www.youtube.com/v/jrJ7aU-n1L8&hl=en&fs=1&"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="www.youtube.com/v/jrJ7aU-n1L8&hl=en&fs=1&" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="560" height="340"></embed></object>[/youtube]

This projection of overwhelming force at big events is becoming more common. At last year’s Republican National Convention in Minneapolis, police conducted peremptory raids on the homes of protesters before the convention began. In all, 672 people were jailed, including at least 39 journalists. According to the Minneapolis Star-Tribune, 442 of those 672 later had their charges either dropped or dismissed.Four years before that, more than 1,800 people were arrested at the previous Republican National Convention in New York City. Ninety percent were never charged with a crime. One notorious photo from the 2008 Democratic National Convention in Denver shows a small mass of protesters, zoned far off from where any delegates or media representatives could hear them, surrounded by two walls of riot police who outnumbered them at least 2 to 1. Denver’s police union later issued a commemorative T-shirt of the event emblazoned with an illustration of a menacing cop wielding a baton and the slogan, “We get up early to beat the crowds.”