One caveat to point out--although a properly executed liability waiver will often extinguish an action brought by the person who signed it (or his estate), it will generally not preclude an action from family members claiming loss of consortium. The rationale is that people can sign away their own rights, but not the rights of others.
Also, a waiver may not be effective for minors who are not usually deemed to have legal capacity to enter into contracts, regardless of whether a parent or guardian signs for them.
All of this varies by jurisdiction and local law. From the perspective of the club, the match organizers and staff, having everybody on the premises sign a nice tight waiver is still a good idea.