Against Hawaii, however, Williams averaged 10.3 yards per carry after starter Michael Alisa was injured in the first quarter.
"It felt pretty good having [the coaches] trust me," Williams said. "It seems like they believe in me."
Coach Bronco Mendenhall called Williams "a really good athlete" with "great vision" who "made the most of his opportunity" against Hawaii. Of course, the Warriors' defense is one of the worst in the country.
BYU gained 540 yards of total offense and piled up 30 first downs.
In losses to USC, Nevada and the Cougars, Hawaii has allowed 1,590 yards and 165 points.
"We couldn't get it going defensively," said Warrior coach Norm Chow.
For good reason, Mendenhall warned everyone not to go "too far on the Jamaal bandwagon," until he consistently produces against defenses like Utah State, Notre Dame, Oregon State and Georgia Tech.
"But we're encouraged tonight," Mendenhall said.
Williams got his big chance when Alisa, the junior starter, broke his right forearm.
On BYU's opening 77-yard drive for a touchdown, Alisa carried the ball twice.
He gained five yards to push BYU across midfield. Then, on second down from the Hawaii 9-yard line, he gained seven yards on a sweep.
Alisa was injured in the pileup, however, and Williams scored from the one with 10:43 left in the first quarter.
"When they told me he was hurt," Williams said, "I knew I had to step up and play my role running or blocking protection."
Williams ran. And ran. And ran.
He helped BYU's offense hold the ball for almost 36 minutes and demonstrated the kind of ability he has flashed.
"We've seen it with the touches he has gotten," Mendenhall said. "But Mike Alisa has been our featured back."
No longer, perhaps.