The troublemakers are often recruited by and sometimes are the undercover cops to incite disturbances and give an excuse to break the demonstration.

The reason that the G20 is being targeted has to do with the policies surrounding the treatment of poor countries (abusive lending practices) and environmental policies that are destructive. Also, slave labor in foreign countries with the eradication of unions, there.

Who the so-called anarchists are is unclear.

Remember that this was a suggestion made in Wisconsin by the Governor who considered breaking that demonstration by introducing troublemakers but for political reasons passed on it. He thought that it would put too much sympathy
on the side of the Union and against his tyrannical bill.