2. Edmond Taverdyan
Olympic judo medalist Ronda Rousey became a superstar as she dominated the UFC women’s bantamweight division. Her coach, Taverdyan, took a lot of credit for her success. But he failed to help her evolve and adapt to different fighting styles. He also encouraged her to throw her hands in a fatal error (via Sportskeeda).
She fought Holly Holm in a title defense that went badly wrong. Holm lit her up on the feet in an electric display. But Taverdyan infamously told Rousey that she was doing well and encouraged her to box. Remember, Rousey was an Olympic medal-winning judoka. After the fight, Rousey never won in the UFC again and much of that blame was placed on Tarverdyan.