Jon-Eric Sullivan, Green Bay's director of college scouting, said the Packers have been following Williams for several years and were impressed by his production in 2016 after he withdrew from school in 2015 and skipped that season. Williams played in 10 of BYU's 13 games last season but still rushed for 1,375 yards and 12 touchdowns.
He was No. 5 nationally in rushing yards per game and set a school record for single-game rushing yards with 286 against Toledo. He finished his career rushing 26 times for 210 yards in BYU's 24-21 win over Wyoming in the 2016 Poinsettia Bowl.
"He's an aggressive, downhill runner. He's tough. He's built to last. We are excited about him. We think we got a good football player, a guy who complements the guys we've already got here," Sullivan said. "He's durable. Up here in the elements, he's a good get for us. When it gets cold, he's a good football player."
Sullivan said the club wasn't frightened away by a knee injury that cut short Williams' junior season in 2014.
"We were fine with it," he said, referencing Williams' production in 2016.
In the conference call with the Green Bay media, Williams was asked what he did to violate BYU's honor code before the 2015 season and he told them he "had a girl in my room." Asked how NFL general managers and coaches reacted to that news, Williams said "most of them laughed with a surprise on their face."
Williams said he returned to BYU out of a sense of loyalty to the school because it was one of the few that recruited him out of Summit High in Fontana, Calif.
Williams is the first BYU running back drafted since Harvey Unga was picked in the 2010 supplemental draft by the Chicago Bears.
"Can't wait to see Jamaal doing the Lambeau Leap!," BYU athletic director Tom Holmoe wrote on Twitter.
Sullivan said Green Bay wasn't scared off by Williams' withdrawal from school.
"He had an honor code violation," Sullivan said. "We feel really good about the kid. He is well-liked by his teammates. He's a team captain. Football is very important to him. He does the little things to be a good football player."
Williams said he didn't have much contact with the Packers before the draft, other than a visit with running backs coach Ben Sirmans at the NFL combine in February.
"I feel like a big weight has been lifted off me," Williams said. "I am just grateful to be off the board and have a team like the Packers pick me."
BYU coach Kalani Sitake said in a school news release that Williams has the ability to play at the next level.
"His style and abilities as a tough, decisive runner and good pass protector will translate extremely well to the NFL game," Sitake said.
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