There are people who firmly believe women can never outcompete men due to biology. With some outliers, this is currently true within a defined age range and only in certain sports (there are several where women routinely outclass men). In 6th grade a good chunk of the boys haven’t hit puberty yet and you can easily find girls who are stronger, faster, and more athletic than boys in their cohort because everyone is still developing. The boys getting beat right now could hit a growth spurt next week and play in the NBA.
The point is at this age, the kids are actually pretty evenly matched. If the boys have a violence problem, they should be banned from playing till they fix it. Otherwise this league head should shut the fuck up.