AMHERST, Mass. — True freshman running back Jackson McChesney didn’t touch the football until BYU’s fifth possession Saturday afternoon against UMass.

With just under 12 minutes remaining in the second quarter of the Cougars’ eventual 56-24 win, McChesney rushed for four yards in his first carry since mop-up duty last weekend against Idaho State.

Then he exploded, as it were.

McChesney finished with 228 yards and two touchdowns on 15 carries to break the BYU freshman record for single-game rushing yards. His 228-yard performance was the sixth-best all-time at BYU.

“Kinda like Zach (Wilson) was saying, the offensive line was opening up the holes,” McChesney said. “Guys like (fullback/tight end) Masen Wake were throwing their bodies in front of people just so we could get through.”

Another backup, Tyler Allgeier, added 37 yards and Lopini Katoa chipped in 34 as the Cougars racked up 320 yards on the ground against the overmatched Minutemen.

“I am just trying to do what I can do, do my 1/11th,” said McChesney, who will still redshirt this season because he’s played in only two games and can play in four and still preserve that status. “Coaches are always saying that if everybody does their job, we are going to do great things.”

Theoretically, McChesney could break his own record, because he will be a redshirt freshman next year. On his second carry Saturday, the Lone Peak product broke through the line of scrimmage, plowed over a UMass defensive back, and sprinted 44 yards to the end zone before showing he’s no quarterback.

“Coaches are always saying that if everybody does their job, we are going to do great things.” — BYU running back Jackson McChesney

“It felt really good,” he said. “I just lowered my shoulder on that guy and I was still on my feet. I finally went into the end zone and grabbed the ball and threw it over the referee’s head, (because) I was so excited to be in the end zone for the first time.”

As reported by the Deseret News on Friday, Cougars redshirt running back Sione Finau, who rushed for more than 100 yards last week, sustained a season-ending knee injury in practice on Tuesday. Allgeier was moved from linebacker to running back, and McChesney was moved up the depth chart. The situation was dire because first-string RB Katoa was considered a game time decision due to being in concussion protocol earlier in the week.

Katoa started, and had a pair of nice runs before Allgeier’s 57-yard catch-and-run put the Cougars on the board. Katoa scored BYU’s second touchdown on a 3-yard run, then its fourth on a 14-yard screen pass.

Then McChesney took over.

“We knew we were going to try to redshirt him and stay within the four-game limit for what he can do,” head coach Kalani Sitake said. “He is still not 100% yet. He’s trying to get back and get healthy, still has the mission legs. He is trying to get back his old legs like he had at Lone Peak.”

In the second half, when UMass had its first-teamers on the field but BYU had gone to its second- and third-stringers, McChesney rattled off a 62-yard run and followed that with a 12-yard touchdown run.

That time, he didn’t overthrow the official. Wilson was impressed.

“I mean, these (running backs) have grit,” Wilson said. “Every day in practice, they are the most disciplined group, the most focused and ready-to-go group. They bring the juice every day. I am not surprised that guys like Jackson stepped up. He’s a heckuva player. He’s got great speed and it really starts with those big boys up front.”

Sitake confirmed that Finau is out for the season, but said Emmanuel Esukpa (toe injury) might be able to play next week to take some pressure off Katoa and McChesney.

Defensively, the Cougars played without starting safety Austin Lee, starting cornerback Chris Wilcox and valuable defensive lineman Lorenzo Fauatea. All three should be able to play next week, Sitake said.

Defensive tackle Bracken El-Bakri left the game in the first half with an apparent injury and was wearing a protective boot on his right foot after the game.