The league is also asking football coaches to spend more time emphasizing and teaching techniques for avoiding helmet hits and show videos of permissible and nonpermissible hits.

Some coaches in the eight-team Ivy League have already been limiting the number of full-contact practice sessions, and rules are in place to examine players and remove them from games if they have sustained severe head hits or concussions. The new rules, however, will prevent existing or new coaches from adding full-contact practices, Harris said.

“I’m not sure there will be any dramatic changes, because the changes over the last few years for dealing with head hits have changed dramatically,” said Tim Murphy, the football coach at Harvard. “If we want young people to continue to fall in love with this great sport, we have to protect the athletes.”

Murphy said that reducing the amount of contact during the week will not only reduce the chance of head trauma, but also keep his players fresher on game days. Too much contact in practice can lead to diminishing returns, he said. Murphy added that he did not think that the stricter rules will have any impact on recruiting.

During a full season of practice, each team tracked in the study published by the Journal of Athletic Training averaged 2,500 total hits to the head that measured as significant blows (50 to 79 g’s of force) and about 300 hits to the head that were considered in the concussion-causing range (80 to 119 g’s). Each team experienced almost 200 practice collisions that measured above 120 g’s, which experts have likened to crashing a car into a concrete wall at 40 miles an hour.

The Ivy League does not have league-wide statistics on the number of concussions and head hits that occur during practices or games because the universities track them differently. But in more than 40 games involving Ivy League teams last year, eight penalties were assessed for helmet hits or blows to the head. Four other penalties were handed out for hits to a defenseless player. In all, 0.18 percent of plays involved significant helmet hits or hits to the head, according to the league’s data.

Several schools and conferences have re-evaluated their protocols concerning head injuries in recent years, although restrictions on practices like those being implemented by the Ivy League are considered rare, if not unprecedented.

“We worry about it, and it seems we should err on the side of caution,” said Margot Putukian, the director of athletic medicine at Princeton University. “My hope is that this will work at Penn State, too.”