Beggs, a student at Euless Trinity High School near Dallas, is a female transitioning to a male and is taking what is reported to be a low-dose of testosterone, according to the New York Post.
Beggs (36-0), who won last year's Class 6A girls championship in the 110-pound division, won by decision 15-3 against Chelsea Sanchez of Katy Morton Ranch.
"He has so much respect for all the girls he wrestles", Beggs' mother, Angela McNew told the AP.
"People think Mack has been beating up on girls ..."
"You put me in front of anybody and I'll wrestle them", Beggs said. "It has more to do with skill and discipline than strength".
Beggs had tried to compete in the boys division but was knocked back by the State, which now says that athletes can only compete in the gender determined by their birth certificate. However, he completes in the girl's division because Texas public high schools require athletes to go by the sex on their birth certificate.
"I understand if you want to transition your gender", she said. "All I can hope for is that they come to their [senses] and realize this is stupid and we should change the policies to conform to other people in my position".
You can do that after high school.
"If he has been taking hormones or steroids, he should be wrestling boys", Roush argued, according to CNN.
Texas laws ban performance enhancing drugs for high school athletes, but there is an exception if it is taken for medical purposes.
Beggs' road to the championship last season included two forfeits in the regional tournament by wrestlers who feared injury.
Parents are reportedly concerned about the safety risk of their children competing with an athlete on steroids, with more than one opponent forfeiting against Beggs.
Emory University Department of Orthopedics assistant professor, Dr. Brandon Mines, agreed with several other parents at the match, maintaining that Beggs should compete with boys instead of girls.
Beggs told the Dallas Morning News' Sports Day that she had been forced to compete against girls. It transformed his physical appearance and added muscle mass.
The 18-year-old returns to the finals facing less drama than he did last year. It's been a lot quieter since a year ago when his march to a state championship was dogged by a last-minute lawsuit that tried to stop him.
Beggs is now entertaining a scholarship offer at an out-of-state school. "I would rather have a chance to compete than not compete at all".