Alaskan female bear(sow) attacks a male bear(boar) for looking at her cubs.

Sow with three cubs taking a big boar's fishing spot. He was there first. Video taken by Martin Boland at Katmai National Park Alaska, on one of Scenic Bear Viewing tours with clients.
Male bears sometimes kill the cubs so they can mate with the female during mating season. This is not mating season but the mom does not care. They trust humans near their cubs more than any other bears where we go. People have been bear viewing in this park for over 30 years without any injuries to bears or people on any professionally guided tour. These bears have never been hunted, harassed or feed by humans so we have a very neutral relationship with them.