Transgender MMA Fighter Sends Female Opponent to Hospital

I don't follow MMA (Mixed Martial Arts) however this story caught my eye. I'm all for equal rights and woman competing in everything men do, but where does something like this fall? Fallon Fox with a record of 5-1 began her life as a man... but got a sex change in 2006. This was not known until 2013 after she has won her first two fights by knockout in the first rounds. There were many critics of Fox fighting agains woman since she used to be a man and physiologically still is one. Since her past was reviled she has won 3 more fights and suffered her first loss. Over the weekend the controversy flared up due to her winning her latest fight only lasting 3 minutes and sending her opponent to the hospital with a concussion, broken orbital bone and receiving 7 staples in her head after the fight. I do understand that injuries like this can happen no mater who is fighting is such a sport as MMA and some studies state that Fox has very little advantage if any due to the low testosterone in her body. I'm just wondering where the line is drawn on where a man ends and a woman begins when it comes to athletics?