Moving kickoffs from the 35-yard line to the 40-yard-line seems to have sharply reduced the rate of concussions in Ivy League football, a new study led by University of Pennsylvania researchers found.

In the two seasons since the 2016 rule change took effect for the eight Ivy schools, the researchers counted two concussions per 1,000 kickoffs, down from 11 concussions per 1,000 kickoffs during the three seasons before that.

By kicking from the 40-yard-line — five yards closer to the other team's territory — kickers had a better chance of booting the ball into their opponent's end zone. That meant the receiving team had the option of settling for a collision-free touchback — automatically placing the ball at their 20-yard-line instead of running the ball toward the slew of oncoming tacklers.

After the rule change, nearly half of kickoffs resulted in touchbacks, up from just 18 percent previously, said the Penn study authors, who collaborated with researchers from the league and Princeton University. Their analysis of the rules change was published Monday in the Journal of the American Medical Association.

"There's very compelling evidence that it dramatically reduced the rate of concussion," said Douglas J. Wiebe, lead author of the study and a professor of epidemiology at Penn's Perelman School of Medicine.

Football officials at all levels have been criticized for doing too little to prevent concussions in what is inherently a violent game. In 2015, the NFL settled a lawsuit with former players who claimed they had suffered cognitive impairment from repeated collisions on the field. Yet now that leagues have implemented a variety of rules changes, some die-hard fans complain the game has become too soft.

At the college level, kickoffs may become even safer after broader rule changes that took effect this year. The NCAA, which includes the Ivy League, now allows a kickoff receiver to declare a fair catch anywhere inside the 25-yard-line, meaning he cannot be tackled and the ball is placed at the 25.

However, kickoffs at most NCAA schools still are made from the 35-yard-line, not the closer 40-yard-line that remains in effect for the Ivies.

The NFL has tweaked its kickoff rules, as well, but with a different approach.  Among the changes: The kicking team is no longer allowed to get a running start, and eight of the 11 players on the return team must line up in a "setup zone" within 15 yards of where the ball is kicked. In addition, no hitting is allowed in the setup zone until the ball is caught or hits the ground.

Asked about the study on the Ivy League, the NFL did return a request for comment.

The rules change in the Ivies came after coaches learned that kickoffs accounted for 21 percent of concussions, though they represented just 6 percent of all plays.

Wiebe said he was impressed by the proactive approach.

"It's quite innovative for an athletic conference to say 'Let's do this,'" Wiebe said. "I think this is a real injury epidemiology public-health success story."

The study was published after a weekend of grim head-injury news from the gridiron.

A Georgia high school football player died Sunday after sustaining a head injury in a Friday game, according to CNN. Earlier Sunday in Long Island, a 6-year-old was airlifted from a football game after suffering a head injury.