There is a lot of uncertainty about how the new kickoff rules in college football will affect games.

The rules makers are hoping for more touchbacks and fewer concussions, which is exactly what happened with a similar change last year in the NFL.

Coaches anticipate some added intrigue, too, as teams weigh the risks and benefits of kicking the ball high and short of the goal line to force the opponent to earn its field position.

The changes: the ball will be kicked off from the 35-yard line instead of the 30, defenders will get only a 5-yard running start and touchbacks (on kickoffs only) will result in the ball being placed at the 25-yard line instead of the 20. It’s the last part of the rule that raises questions — that’s 5 yards of field position that coaches aren’t sure they want to surrender.

“If you knew you could consistently tackle them inside the 25, I’d take 3 or 4 more yards of field position,” Air Force coach Troy Calhoun said. “You never know, that may be an extra field goal as you play.”

Last year, Boise State led the Mountain West with a net average of 46.4 yards per kickoff. Under the new rules, that would result in opponents starting at their own 19-yard line. Kickoff specialist Trevor Harman, who recorded 17 touchbacks last season, returns and figures he could regularly force touchbacks with low, driving kicks if that’s what coaches want.

Boise State coach Chris Petersen says he’ll do what’s best for field position — sometimes that might mean forcing a touchback, and sometimes it might mean forcing a return.

“If we had our druthers, if we could predict it, we’d want to mix it up,” he said.

A study released this month indicated that concussions sustained on NFL kickoffs dropped from 35 in 2010 to 20 in 2011 with the new kickoff rule. Touchbacks spiked considerably, to nearly half of all kickoffs.

CAMP IMPRESSIONS

• In the Wednesday morning practice, senior tailback D.J. Harper reached behind himself with his right arm to make a one-handed catch on a crossing route. Freshman defensive end Sam Ukwuachu added an interception on a screen pass.

• In the afternoon, the first-, second- and third-team offenses failed to get within field-goal range in game-like drives. Defensive end Tyler Horn foiled the first-teamers with a sack and safety Darian Thompson stopped the second-teamers with an interception.

• The veteran wide receivers — seniors Mitch Burroughs and Chris Potter, junior Kirby Moore and sophomore Matt Miller — have impressed throughout camp. Potter and Moore have been the last two campers of the day selected by Petersen.

SPOTLIGHT ON … DE BEAU MARTIN

Boise State sophomore Beau Martin, who transferred last year from Colorado State Pueblo, is competing with redshirt freshman Sam Ukwuachu and junior Kharyee Marshall for playing time at the stud defensive end position, the spot played by Shea McClellin in recent years.

Martin, a walk-on, has a strong chance to win the job.

“The thing I’m most excited about is I learn so much each day,” he said. “We get so much done in our meetings that I walk away at night really feeling like I’m getting a little better. And if I can do that every day, then I think I’m getting closer to where I need to be.”

Martin (6-foot-2, 250 pounds) is part of a raw collection of ends on the Broncos’ roster. Six of them haven’t played major college football and neither of the other two have played extensively.

Martin came to Boise State because he didn’t want to settle for playing at a lower level. Now he’s a couple weeks from his debut.

“I couldn’t be more excited,” he said. “I love this game so much. It is a great opportunity. It’s just an opportunity that I’m glad that I have. Of course, you’re nervous, but that’s a good thing. That means that you really care about this game, and I do.”

MEANWHILE, AT NEW MEXICO …

Quarterback B.R. Holbrook left practice early Wednesday for the second straight day with shortness of breath and tightness in his chest, according to KRQE. He has left the Ruidoso, N.M., training camp to be evaluated in Albuquerque. Holbrook started the final eight games last season.

Chadd Cripe: 377-6398, Twitter: @IDS_BroncoBeat