Abbie Hoffman is perhaps most well known as the leader of the Chicago Seven, a group of radicals who led protests that included violent confrontations with officers at the 1968 Democratic National Convention.

That same year at the height of the counter-culture revolution, Hoffman published "Revolution for the Hell of It," a book and motto that also fits today's Black bloc anarchists.

Black-bloc anarchist tactics are believed to have originated in Germany in the 1980s, before spreading throughout Western Europe. These anarchists are bent on chaos, mayhem, and revolution. They often infiltrate legitimate protests and, on cue, begin vandalizing, setting fires, making barricades, as well as rioting and battling police.

Black bloc members can be identified by their signature uniform—all black clothing, bandannas or masks covering their faces, backpacks, and sometimes motorcycle helmets. Inside the backpacks, they often carry hammers (to smash windows), flares, and other gear.

Law enforcement first became aware of black-bloc anarchists during the 1991 Gulf War protests and, in a more pronounced way, during the 1999 WTO rioting in Seattle. Since then, black-bloc anarchists have wreaked havoc in a growing number of U.S., Canadian, and European cities. The following is a partial list of cities where black-bloc tactics have been used:

2001: Genoa, Italy. G-20 Summit protests.

2003-04: Various U.S. cities, including San Francisco. Anti-Iraq/Afghanistan War demonstrations.

2007: Quebec, Canada. G-20 Summit demonstrations.

2009: Germany. Protests.

2009: Pittsburgh, Penn. G-20 Summit. More than 4,000 officers from throughout the U.S. were involved.

2010: Vancouver, British Columbia, Canada. Anti-Olympics demonstrations.

2010: Toronto, Ontario, Canada. G-20 protests. Largest number of officers in Canadian history involved.

2011: San Francisco. A series of near riots stemming from protests over another BART Police shooting.

I've saved the latest black-bloc violence in Oakland, Calif., for last:

2009: In January, two separate riots in downtown Oakland were related to the Oscar Grant shooting by a BART Police officer.

2010: Two, separate riots in downtown Oakland were related to the Oscar Grant shooting.

2011: Two riots in less than two weeks in downtown Oakland, related to the Occupy Oakland movement.

That's a total of six riots in downtown Oakland since 2009. And in each one of these riots, black-bloc tactics were at the forefront of the violent rioting that resulted in hundreds of arrests, numerous injuries, and massive property damage. Not to mention the spiraling costs to cities to provide police and sanitation services.

Policing the riots makes up much of the cost, which has placed an extreme financial burden on cash-strapped Oakland. The mutual-aid costs from surrounding law enforcement agencies will be paid for by the equally cash-strapped state of California. Mutual aid is a necessity for the Oakland PD, which has employs about 650 officers for a city of about 396,500 residents with a crime rate that consistently ranks in the top 10 of cities in the U.S.

Even though anarchists who use black-bloc tactics are relatively few in number, their strategy and tactics of wreaking havoc, chaos and mayhem provides them with the sensational news coverage they crave. They often infiltrate, then try to hijack otherwise legitimate causes. They try to do whatever they possibly can to make police look bad. They try goading them into overreacting, preferably while cameras are rolling. This is done to portray rioters as victims of police brutality.

Anarchists, especially adrenaline-charged anarchists, thrive on violent confrontation and the resultant media publicity. The more, the better—especially on live TV. Naturally, the media is drawn to live-action events, especially involving police action and violence. The more sensational, violent and controversial the situation, the more media coverage is generated.

Conversely, police are duty bound to act within the law and follow departmental rules and regulations. This often requires tremendous self- discipline and restraint, especially in the face of extreme provocation and attack (physically and verbally).

From where I sit, police in Oakland have acted with great professionalism and restraint. Officers used force only after being physically attacked by anarchists-turned-rioters who hurled rocks, bottles and paint. They broke windows, started fires, and were responsible for other extreme, provocative, and lawless acts.

What's next for Oakland is any one's guess. However, if its recent history is any indicator, Oakland has not seen the last of the anarchists who foment "revolution for the hell of it."