This is another repeatable quest that will be triggered when you visit one of your settlements on the Island. First, they'll tell you about an impending trapper attack. You'll have a brief time to set up your defenses and wait for their attack. Once their attack begins, hold your ground and do your best to repel their attack. Once done, talk to the settler that reported to you. He/she will tell you the location of the trappers that attacked the settlement. The settler will offer to come along with you and you have the option to accept the help or wipe out the trappers alone.