If its brave... Set some stinky canned cat food out, and wait.... BANG!!!!no more raccoon problem. I've heard they can eat a whole bird through a 1/2in hole.
Used dog kennels work pretty well in a pinch. Easy to move and setup. Fairly safe from predators. In my experience, ducks just sleep on the ground or on the ramp to the pool.
If one started pecking at it, they all certainly might join in. You'll probably have to sit and observe behavior for awhile to figure out who's the offender. Some birds are just buttheads. Maybe move some to a separate coop. Hope you find the bully!