UCLA vs. BYU: This might be a first for freshman quarterbacks

Las Vegas bookmakers view No. 10 UCLA vs. No. 19 Brigham Young as a Bruins breeze. UCLA is a 16 1/2-point favorite. The prediction here is that the game will probably be closer when the teams get on the field at the Rose Bowl Saturday. Times staff writer Chris Foster examines the game’s matchups and storylines:

Frosh, by gosh

This could be the first meeting between ranked teams led by first-year freshman quarterbacks.

However, that distinction comes with an asterisk.

BYU’s Tanner Mangum is 22 years old, having spent the past two years on a Mormon mission in Antofagasta, a port city in Northern Chile. UCLA’s Josh Rosen was a freshman at Bellflower St. John Bosco High when Mangum was a senior at Eagle (Idaho) High in 2012.

That should take none of the luster off Mangum’s rocket-like rise. The Cougars season had barely started when it seemed to crash. Quarterback Taysom Hill suffered a season-ending injury in the opener. Mangum came off the bench and had a Hail Mary (pass) answered to beat Nebraska. Last week, his last-minute touchdown pass downed Boise State.

Rosen has done nothing in outings against Virginia and Nevada Las Vegas to tamp down the preseason hype about him. Given how well the Cougars play the run — they limit opponents to 95 yards rushing per game — Rosen may need to produce even more in this one.

Perseverance

UCLA Coach Jim Mora expressed concern about Mangum’s ability to freelance. His ability to extend plays puts more stress on the secondary.

The Bruins have one sack in two games but have applied pressure on quarterbacks. They need more of that Saturday.

Things that go bump

The quarterbacks, as always, have the spotlight. But this is expected to be a fierce fight in the trenches.

BYU has muscle on both sides of the ball. The offensive line averages 306.4 pounds. Defensive end Bronson Kaufusi is 6 feet 8, 280 pounds. Harvey Langi is a 240-pound linebacker who has three sacks in two games. Fred Warner is a handful at outside linebacker.

There was a time UCLA was considered soft. Anyone who says that now has not seen the Bruins play recently. One key for UCLA will be how well Eli Ankou and Matt Dickerson can fill in at defensive tackle for Eddie Vanderdoes, who sustained a season-ending injury in the Bruins’ opener.

Secondary is primary

An area of concern for the Cougars is the secondary. Cornerback Michael Davis is the only returning starter for a unit that is giving up an average of 308 yards passing per game.

Run down

BYU’s running game took a hit before the season began. Senior running back Jamaal Williams, who had 2,526 yards and 23 touchdowns in his career, withdrew from school in August.

The Cougars still have not quite found their footing. Adam Hine leads BYU with 130 yards in two games, but the team’s other running backs have gained 31 yards and lost 17.

UCLA’s running game, led by Paul Perkins, is averaging 213 yards per game.

chris.foster@latimes.com