And when a basketball player has the ball he is the only one with the ball, as there is only one ball. When he has to shoot at the buzzer to win the game, is he suddenly playing a solo sport?
Boxing is CLEARLY a team sport: It takes a fighter, a rich promoter, a corrupt ref, three corrupt judges, etc ......
Solo. Of course you need a team around you but once you get in the ring, it's just you and your opponent.