Have you observed bullying behavior or are you just assuming it?
The sudden appearance of feathers from a couple of the chickens may simply be from molt. Examine the chickens. Look for pin feathers emerging from the bald spots. This is what molt looks like. If the feathers are frayed and broken with no evidence of re-growth, then it is probably from rough-housing.
If you identify bullying, then you need to observe further to identify the bullies. Placing the bullies in confinement for a few days may help solve the problem. If not, then you can resort to pinless peepers for the bullies so they're less apt to snatch feathers.