12 players who will define Boise State's first Pac-12 season: No. 12, Sire Gaines

The fall camp countdown clock is officially on for Boise State’s historic 2026 season.

The Broncos were among a group of five Mountain West schools that officially joined the Pac-12 earlier this month.

In the lead-up to fall camp, Boise State Broncos On SI is highlighting the 12 players who will define the Broncos’ first season in the reborn Pac-12.

To kick off the series, we will break down bruising sophomore running back Sire Gaines.

Recapping Gaines’ 2025 season

Coming off a promising true freshman season that ended early due to injury, Gaines was expected to be Ashton Jeanty’s primary replacement at running back as a redshirt freshman in 2025.

Gaines, a 6-foot, 217-pound power back, was usurped on the depth chart by speedster Dylan Riley but still had 161 carries for 811 yards and nine total touchdowns in a supporting role. Gaines had nine or more carries in 10 of Boise State’s 14 games and ran for a career-high 149 yards on 22 attempts in a blowout November win over Colorado State.

Gaines earned two Mountain West Freshman of the Week honors last season and received a Pro Football Focus rushing grade of 88.9, ranking No. 1 in the MWC and No. 13 nationally.

Why Boise State is counting on Gaines in 2026

The Broncos are deep at running back with Gaines, Riley and transfers Juelz Goff (Pittsburgh) and Harry Stewart III (Kansas), but Gaines’ combination of size, power and tackle-breaking ability stands out among the group.

Gaines, the thunder to Riley’s lightning, ranked third in the MWC last season with 46 missed tackles forced. Gaines led the conference with a 49 percent success rate on short-yardage runs and had 58 carries result in a first down, ranking third in the MWC.

While the Broncos can lean on Riley’s versatility and home-run ability, Gaines brings a level of physicality that wears down opposing defenses. He pairs perfectly with Riley to create a one-two backfield punch that is unmatched in the new Pac-12.

Gaines’ 2026 outlook

Gaines finished 189 yards shy of a 1,000-yard rushing season in 2025 despite a three-carry game against Air Force and a six-carry day in a blowout victory over UNLV.

If Gaines can stay healthy, he should steam right by the 1,000-yard mark this season and make the all-Pac-12 team alongside Riley.

Gaines, who enters this year with 14 career catches for 116 yards and two touchdowns, could also become a bigger factor in the receiving game.

See our full list of 12 players who will define Boise State’s first Pac-12 season:

• No. 12 - Running back Sire Gaines, sophomore

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