Troy Calhoun.jpg

Air Force coach Troy Calhoun is backtracking on whether the 10-second substitution rule should be implemented next season based on safety.

Air Force coach Troy Calhoun, chairman of the NCAA Football Rules Committee, has expressed concern there's not evidence to support a proposal allowing defenses 10 seconds to substitute before offenses snap the ball.

In two national interviews this week, Calhoun raised doubts about the rule as a safety precaution. The proposal caused an uproar within the coaching community, especially by up-tempo coaches such as Gus Malzahn, who wants to table the rule until next year.

Calhoun previously said the committee "felt like it was time to act in the interests of protecting our student-athletes." But on the Tim Brando show this week on SiriusXM, Calhoun said, "If there is no medical data that can support it, then there's no way. There should not be a rule. Now, if you go and there's truly ... a resounding concern by people who should have the right insight and right background from the medical community that, indeed, if you don't have a substitution pattern in place or be able to provide adequate rest and recovery for somebody, then I think you have an obligation to bring that up."

In hindsight, Calhoun told Brando he doesn't think the rules committee had enough of the medical community at the meeting to inform members. Many medical personnel and researchers say there could be health benefits, but there's no evidence.

Brando told Calhoun that he believes Alabama coach Nick Saban and Arkansas coach Bret Bielema carried influence with rules committee members by speaking at the meeting in favor of defensive substitutions.

"I can certainly see why you may induce that," Calhoun said. "But it's still got to be solely, is it a medical concern? ... The strategic part cannot be a factor at all. That is the part that's going to arouse interest is the strategic part of it."

The proposal must be passed by the Playing Rules Oversight Panel. The football rules committee has the ability to pull the proposal before PROP hears it on March 6.

Calhoun told ESPN.com's Brett McMurphy that a "group" at the University of North Carolina and the NCAA may present injury information before PROP committee members vote in two weeks. Calhoun said there's "genuine concern" about whether an injured player can get off the field, and a counterargument is teams can use a timeout.

Stefan Duma, a professor at the Virginia Tech-Wake Forest School of Biomedical Engineering and Sciences who studies football brain trauma, said the tempo question is interesting but knows of no studies supporting the rule proposal.

"When the NFL changed kickoff rules, they had pretty good data on the concussion rate on kickoffs," Duma said. "I think it would be great if we could have that on this discussion. I think this is just very anecdotal."

The rules debate isn't happening in a vacuum. The NCAA and its schools face legal threats over their handling of concussions, raising a question of whether the NCAA would kill this proposal after the rules committee initially supported it for safety purposes.

Duma likens the NCAA's situation to the debate a couple decades ago about whether to install air bags in cars. When he was a graduate student, Duma asked an engineer at Chrysler if he was worried about being sued if the company didn't put in air bags.

"He said we're going to get sued no matter what," Duma said. "I think that's the case here. There's going to be lawsuits no matter what you do. You really have to use the science to do what you think is best and let the data show it."

Saban himself once expressed the need for scientific data before making football rules changes related to player safety, such as eliminating the three-point stance.

"I think football is a great team game, probably the greatest team game there is," Saban said at the SEC spring meetings in 2012 after Junior Seau's suicide. "But I certainly would not want to do anything as coaches or teachers to affect somebody's future ability to function in a normal manner. But at the same time I hope the things that are out there right now (about suggested rule changes), there's enough scientific evidence to make sure we're not creating something that maybe we don't overreact to, even though I don't want to do anything that would hurt any player."