RIO DE JANEIRO (AP) — Felled by an opponent’s knee to the head as they both chased the ball, a player is seemingly out cold on a World Cup pitch. The clock is ticking. Millions are watching. National honor, careers and sponsorship dollars are at stake.

Groggily, the player wakes up and argues furiously with his team doctor that he must play on. For anyone attuned to the dangers of concussions and head injuries, this is when alarm bells ring — just as they did when this scenario unfolded at the World Cup in Brazil.