A referee for a recreational soccer league in Salt Lake City is fighting for his life after being struck in the face by a 17-year-old player.

At first, the injuries seemed minor, but "when the man was taken to a hospital, however, they discovered serious internal head injuries," said Justin Hoyal, a police lieutenant, told the AP. The referee has been in critical condition since the incident occurred on Saturday.

The referee is most likely suffering from traumatic brain injury (TBI), a potentially fatal condition. Over 1.5 million people experience TBI each year in the United States, and it ultimately contributes to 1 in 3 injury-related deaths, according to the CDC.

In boxing, concussions are built into the fabric of the sport, but life-threatening brain injuries are surpsingly far more common in sports like cycling or football. Fatalities in boxing do occur, but normally require multiple impacts to the head. The heavyweight Beethavean "Sweet Bee" Scottland famously died one week after sustaining from TBI-causing blows during a grueling 10-round bout with George Jones.

Even a single punch can kill. In February, a former professional boxer was sentenced to 7 years in prison after he killed a stranger with a strong haymaker to the jaw.