Surprisingly calm?! You've got to be kidding. I was knocked over by a police baton charge and landed was almost trampled by peaceful protesters who were literally being pushed down the street by police clubs. I don't know where you were standing, but being at the bottom of a pile of people pushed off their feet by unprovoked police certainly seemed a bit excessive to me. Oh, and by the way--the march had a permit, as well. The police (unsurprisingly) acted completely illegally.
I was ahead of the melee, so could not see what happened. One minute everyone was marching in a calm, joyous manner, the next moment there was a small stampede, which quickly fizzled. I was later told by a National Lawyers Guild rep. that an act of civil disobedience occurred(blocking of an intersection), followed by an overreaction by the LAPD (which I am sure were just waiting for ANY excuse to rush the crowd) and a counter-reaction by marchers.
Except for this incident, I too thought the cops were surprisingly calm during this march---that is, if you ignore the fact that marchers were flanked by hundreds upon hundreds of cops in full riot gear ready to strike at any moment (as was later the case after the Human Needs Not Corporate Greed march). Calm--if you consider overt acts of intimidation to be an acceptable tactic. Perhaps the proper word would be "restraint." By that, I mean that the cops actually allowed, under duress, the march to continue.