UFC Hall of Fame member and former promotion's women's bantamweight champion Ronda Rousey explained her departure from mixed martial arts in 2016.
My concussion history that I had to keep secret for years so I would be able to continue to compete and perform, that's basically why I had to retire. I think that there was just so much to (that loss), that I couldn't talk about it. So much had to do with having so many concussions when I was in judo before I even got into MMA, I couldn't talk about it because it would literally put a target on my head, and I might not have been allowed to compete any further.
Ronda Rousey
The 37-year-old Rousey last fought against Amanda Nunes in December 2016 at UFC 207. In this confrontation, Ronda was defeated by technical knockout in the first round. After this fight, she left the promotion and made her WWE debut in April 2018. She has 12 wins and two losses on her MMA record.