Disclaimer: I'm Australian and our educational landscape is somewhat different.
That said, there are some similarities in that playing sport of some kind is essentially compulsory in most, if not all, private schools, and not necessarily so in most public schools.
And of course, (what we call) rugby union is very popular here, as is rugby league and football.
I am being entirely serious when I say that I would immediately disenrol my child from a school that 'required' him or her to play rugby - or any other sport where there is a reasonable risk of traumatic brain injury inherent to the ordinary course of playing the game. Particularly if said child was under the age of 13.
The lifelong ramifications to brain development resulting from early concussions are such that I seriously question the ethics of any institution that 'requires' a minor child to assume that risk.
Though, from PPs responses, it's apparent that I approach this from a different angle to many.
To me, even 'voluntary' participation of minors is questionable - they cannot possibly apprehend the life-long and potentially life-altering (life-destroying) consequences of early concussion and CTE.
...I mean, in both Australia and the UK, parents can be charged with an offence if they leave a child under the age of 13 home alone for more than a couple of hours, or with responsibility for younger siblings: because they lack the cognition and judgement (and experience) to reliably evaluate and appropriately respond to both ordinary and extroardinary risks to health and safety.
...But somehow those same children (and even younger) are supposed to have the maturity, discernment, foresight and medical comprehension required to evaluate, and then assume, the life-long risk to their health and well-being that early concussions represent.
The research has been coming out for years now and is undeniable.
Parents have a responsibility to not just passively accept 'business as usual' sport participation policies from their children's school.