Some of these things seem to materialize out of thin air, with little or no warning. Even if they had a tactic or took, mobilizing in time might be tough, at least as the start of the ride.
If the police can come up with a reasonable way of stopping nonviolent protesters without undue violence, I’d back them in a heartbeat.
Holding up a hand and saying “Stop!” and then grabbing the cyclist is certainly within reasonable bounds. If the cyclist doesn’t want to stop, and gets hurt when a cop grabs him, TOUGH.
The key will be good intelligence. If the NYPD can get a little bit of notice, maybe an hour or so, they will be able to deploy sufficient officers to the area to carry out an organized response.
I’m thinking of something like lining the crosswalks with officers, and playing it like a big game of Red Rover. Twenty officers holding a rope across 7th Avenue can pretty much put an and to any mass movement of anything, including bicycles. Then when the light turns green, the officers can just walk to the curb and let traffic pass, while they block movement on the side streets (No right on red in NYC, don’tcha know...)
Once things are slowed down and the bicycles have to stop for stoplights, the effectiveness of the mass ride protest will come to an end.