Players lined up at a shorter distance - such as offensive and defensive linemen - will still be allowed to engage in head-on collisions, but from farther away players will have to approach at an angle in practices.
Pop Warner is the first youth sports league to take such steps, Butler said. The organization will also reemphasize an existing rule barring players from leading with their heads when they block and tackle.
Reducing the amount of hitting in practice will cut down on the exposure to potential head injuries, which can be caused by both big hits that lead to concussions and also from smaller, repeated impacts, doctors said.
"This is the best way we know to immediately and instantly cut that exposure," said Julian Bailes, chairman of the Pop Warner Medical Advisory Board and codirector of the NorthShore Neurological Institute in Chicago.
Bailes said doctors worry that concussions can be even more dangerous for young athletes than adults.
"We think so, yes, because of the immature and still developing and remodeling brain," he said.
The rules ensure that all coaches - from the sophisticated to the inexperienced - are forced to practice more safely, said James Kinderknecht, a physician at the Hospital for Special Surgery in New York.
He pointed to a recent Johnson & Johnson study of 752 youth sports coaches that found that 52 percent believed "there is an acceptable amount of contact to the head," such as "getting their bell rung" or "seeing stars" that can be endured without the potential for serious brain injury.
"What they're doing with these rules is setting up a framework to make it less likely for an inexperienced coach to screw up," Kinderknecht said.
Some teams, including the North Philly Hurricanes, already follow these regulations, said Michelle Sills, the team's president. But she has seen others that have players run at each other from 15 feet away to tackle, often with improper, dangerous form.
"Kids don't tackle with their arms. They lead with their heads," Sills said.
In early July Pop Warner plans to release a new training video showing coaches how to teach tackling with the shoulder first, Butler said.
"We have to show them that there is and always has been another way entirely, which is to aim with the head, hit with the shoulder," he said.
While children might not hit with as much force as older football players, brain trauma may come from more than just concussions. Smaller, accumulated hits, some doctors worry, might lead to some of the same long-term cognitive problems.
"We know that subconcussive blows occur and that they can cause changes in the brain structure and brain function," Bailes said.
Local Pop Warner coaches praised the changes.
The amount of full-contact drills tends to decline as players reach higher levels, so it makes sense to reduce such practices for children said Marc Bredell, athletic director of the City Youth Association Gators.
"If you're any kind of football coach and you're concerned with the health and safety of your children, you should be with the new rules," he said.
Pop Warner limits practices to a maximum of two hours per day, and up to 10 hours per week before Labor Day, and six hours per week after.
Contact staff writer Jonathan Tamari at 215-854-5214, firstname.lastname@example.org or follow on Twitter @JonathanTamari.
Staff writer Julie Zauzmer contributed to this article.