The arrests at the Brooklyn Bridge during the Occupy Wall Street march probably could have been avoided had the march been led by seasoned organizers.
The police suckered the marchers into the arrest trap. NYPD was on bullhorns saying if marchers went on the bridge they would be arrested. A march led by experienced organizers wouldn't have entered the trap. They would have stopped at the line then, as thousands backed up behind them and things got tense, negotiated to cross the bridge. That might well have worked.
I helped organize many protests in Los Angeles a few years back, including massive anti-war protests where tens of thousands came. I drove the truck that led several marches. (This was when I was with ANSWER. We've since gone our separate ways, to put it mildly. But that's another story.) During these and other protests, sometimes things got really tense between LAPD and the protesters. Here's the key part. LAPD knew who to talk to and so did we. Lots of negotiations happened before the march so while we might not have been thrilled with each other, we were on speaking terms. This helps when things get tense.
OWS had no leaders. No one was leading the march. They were newbies and got played for suckers. Oh well, learn from that and move on. But it does illustrate why leaderless resistance doesn't work in groups beyond a few isolated people in a cell. At some point, there has to be leaders.