A spate of tragic fatalities has underscored long-running concerns over safety standards in high school American football, where more players die each year than at any other level of the game.

Evan Murray, a 17-year-old quarterback at Warren Hills Regional High School in New Jersey, became the third player to die in as many weeks after suffering a lacerated spleen in a game last Friday.

On September 5, 16-year-old Tyrell Cameron died after sustaining a neck injury during a punt return in a game for Franklin Parish High in Louisiana.

Later in September, 16-year-old linebacker Ben Hamm died in hospital a week after suffering a head injury during a game in Oklahoma.

The trio of fatalities fits into a broader pattern of deaths in high school football, according to figures from the National Center for Catastrophic Sport Injury Research (NCCSIR) at the University of North Carolina.

Over the past 20 years, 77 students have died from direct injuries sustained during high school gridiron games, an average of just under four each year.

Over the same period, there were an additional 172 indirect fatalities, defined as deaths by systemic failures as a result of exertion in a football activity such as heat stroke.

Kristin Kucera, director of the NCCSIR, cautioned that any analysis should take into account the large numbers of students playing the sport -- just under 1.1 million across the United States.

"It is definitely not common," Kucera told AFP. "We of course feel we should be working to prevent any fatality or serious injury or injuries in general. But they are rare."

- Grim peak -

Undeniably, the numbers of fatalities are way down on past figures, when direct deaths each year regularly reached double-digits, hitting a grim peak of 26 in 1968.

For the most part, however, football fatalities are confined to the ranks of high school players.

Since 1995, there have been only five deaths in professional and semi-professional gridiron, and eight in college football.

In pure statistical terms, the risk is greater for college players -- with the fatality rate last year at 1.33 per 100,000 players compared to 0.45 per 100,000 for high school athletes.

The fact that most deaths occur in high school gridiron continues to perplex experts, with various theories advanced for the death toll in the school arena.

One reason cited is older equipment and helmets that may not meet the same safety standards as those used in college or professional gridiron.

Another is that still-developing teenage brains are more susceptible to injury from second-impact syndrome, which occurs when a player suffers a second concussion when not properly recovered from an earlier knock.

Schools also have inconsistent safety standards, with some not requiring specialist trainers and paramedics to be immediately on hand at games.

Terry O'Neil, who runs Practice Like Pros, a group which offers clinics on safer football techniques for young players, said there was a gulf between safety standards at the professional and college level, and the high school arena.

"High school football is the most dangerous level of the game because it is the least regulated," O'Neil told AFP.

"It's the least supervised, standards are virtually non-existent, there's no national governance, the sport is governed state to state, and some states don't even require an ambulance or emergency medical workers on site at games. The medical infrastructure that exists in college and pro football does not exist in high school football."

O'Neil cited the sharp variation in the incidence of head trauma in professional versus school football.

Three percent of head trauma cases in the National Football League occurs in practice sessions; in high school football, 60-75 percent of head trauma happens in training.

"That is a horrific statistic and there is absolutely no reason why it should happen," he said, adding that many schools still hold full contact sessions in practice in contrast to NFL teams, where contact is limited.

- Numbers down -

The recent rash of school fatalities comes amid a national debate about the risks involved in America's most popular sport.

A recent study of deceased NFL players found 96 percent of those tested suffered from the degenerative brain disease known as chronic traumatic encephalopathy (CTE).

In April, the NFL agreed to settle a lawsuit and pay $765 million to about 5,000 former players over health claims.

For many parents, the safety concerns surrounding gridiron appear to already have had an effect in steering children towards other sports.

The number of male high school gridiron players has fallen by around 25,600 in the space of five years, down to 1.08 million this year from 1.1 million in 2010.

At Maplewood Richmond Heights High School in suburban St Louis, school board chiefs ruled in June to disband the gridiron program. Schools in New Jersey and Maine have taken similar decisions this year.

Nelson Mitten, the president of the Maplewood Richmond Heights School Board, told AFP the decision was taken because of a combination of declining interest and concern over injuries.

"The question first popped up when last year we had a significant number of injuries of the students playing football -- an ACL (anterior cruciate ligament) tear, a head injury that put a student out for the rest of the season. A broken ankle and other significant injuries," Mitten said.

"Once we started looking into it, we found that participation numbers had declined to the point where there was not sufficient interest to field a team," he added.

Some schools have sought to exploit technological advances to mitigate risks. Companies such as Shockbox offer monitors placed inside helmets which can measure impact force and signal when a player may be at risk. Those technologies, however, come with a price tag which is not always within reach of a school's budget.

MaryBeth Horodyski, of the National Athletic Trainers' Association, believes the priority is for more athletic trainers -- healthcare professionals trained in sports medicine -- in schools.

"If there is going to be high school football, then there should be definitely athletic trainers on hand," she told AFP.

"Not just at games, but also at all practices ... That would be the number one thing I would recommend to a high school wanting to minimize the risk of injuries."