This guy was always horny and mistress Ronja and mistress Ines did not like it. He had to learn to focus on other things other than sex all the time. That is why the mistresses chose to dominate and humiliate him as much as they could. The best way the knew how to do it was to ballbust him as it was painful and would kill his hard on immediately.
Lady Krasaviza wanted this guy to learn to endure pain as well as to increase his pain threshold. So the mistress chose to kick him in the balls as it was one of the most painful things she could do to him. It made him scream out loud and he was in excruciating pain but slowly by slowly, he started to get used to it and he got better at handling and enduring pain.