Sports defined by one-on-one fighting, including boxing, wrestling, pancration, and the various martial arts.
In the ancient Greek and Roman world, three of these sports -- boxing, wrestling, and pancration -- were fought nude, and though not explicitly erotic, there was genital contact during the contests.
Many men into Frot are also involved in combat sports, and find fighting in general to be erotic.
Please note that those men are not necessarily into cock combat, but may seek a mildly combative element in their love-making.
Please note also that not all men into Frot are also into fighting; some are, and some are not.
See also natural male sex aggression.