You should not use any force until you have no other choice.
You should ONLY draw a weapon when there is no other choice.
You should never draw it for any other reason.
You should never 'show it' as a form of self defense. Draw only to fire!
As a photographer, RETREAT is always in your best interest.
When retreating, toss a couple stink bombs in their direction. Good ol' burning sulfur works greats.
If you're knocked on your a55 and you are about to be stomped on, reload often!
I would also never hit or push back. It seems that those anarchists are also recording and will edit/upload videos that can sway public opinion. For example, if they hit you and you hit them back...they will forward the video of you hitting them to every news station(leaving out the 1st 30seconds when they were threatening and hitting you). You'll look awfully guilty. This is how the occupiers turned some non-protesting citizens against the NYC police.... their out-of-context videos showing the after-effects of their anarchy which made the police look bad. The alphabet media loves taking videos out of context, and loves editing those videos....
Hire a bodyguard, or work together with other photographers. Don't work as an independent. You might need a witness on your side.
You can also contact the local PD on the scene and request to press charges against anyone physically or verbally threatening you. Back off and get them arrested.
If legal in that area, bear or pepper spray is also an effective way of stopping an anarchist loser. I'd also consider a stun gun too.
Some anarchists are allergic to peanut butter. I walk around with an open jar of Peter Pan and a spoon. That seems to clear out that OWS crowd pretty quickly.
Dress like an anarchist and blend in with them. Make 'em think that you're on their side.
Open Carry a Calico Liberty with a 100rd's of 9mm as preventive zombie control.