Foltz and Sadler died in a single-car crash at 11:43 p.m. CT, according to a Waukesha County Sheriff's Department statement. Sadler was driving the car, the sheriff's department said.
LSU kicker Colby Delahoussaye was also in the vehicle at the time of the crash. He was taken to Waukesha Memorial Hospital for treatment. Tigers sports information director Michael Bonnette told ESPN that Delahoussaye needed stitches and suffered burns to his legs.
LSU later released a statement that said Delahoussaye suffered minor injuries and had been released from the hospital.
The sheriff's department said the car lost control on wet pavement, left the road and struck a tree. Speed appears to have played a role in the crash, according to the department, which added that the incident remains under investigation.
Foltz and Sadler had been serving as student instructors at Kohl's Kicking Camp in Wales, Wisconsin, according to a camp spokesman.
"Sam and Mike each had amazing careers as student-athletes in the Big 10 Conference, but more importantly, they were tremendous men off the field," camp director Jamie Kohl said in a statement. "We are so grateful for the opportunity we have had to know these men and their families."
Nebraska coach Mike Riley, quarterback Tommy Armstrong Jr., linebacker Josh Banderas and wide receiver Jordan Westerkamp will not participate in Big Ten media days scheduled for Monday and Tuesday in Chicago, Nebraska announced.
Nebraska players held a vigil in honor of Foltz on Sunday afternoon outside Memorial Stadium. The stadium's scoreboard displayed Foltz's initials. Community members dropped flowers at the foot of the statue that memorializes fallen quarterback Brook Berringer, who died in a plane crash 20 years ago this April.
Riley was away from Lincoln when he learned the news of Foltz's death. His first call went to place kicker Drew Brown, who was in Wisconsin with Foltz over the weekend. Riley and Brown talked several times Sunday as both traveled toward Lincoln before the Cornhuskers met as a team with their coach in the evening.
Armstrong offered poignant comments, Riley said Sunday night in a session with media after a team meeting.
"My main focus is just seeing [the players] as much as what I say to them," Riley said. "It's impossible for me to say anything to make [them] feel better. That is not the purpose of this. It is just to be together. I wanted to see them and just let them [know] that everybody understands their grief."
The Big Ten Network tweeted condolences to the families of Foltz and Sadler. Michigan State coach Mark Dantonio and Riley posted their thoughts on Sadler and Foltz, respectively.
Our condolences to the families of Sam Foltz and Mike Sadler as well as to the Nebraska and Michigan State communities.— Big Ten Network (@BigTenNetwork) July 24, 2016
In a statement in which he expressed sympathy to the Foltz family and Nebraska, Dantonio added, "Mike impacted so many people, not only as a football player but also from an academic standpoint and in the community as well. The world has lost a rising star who dreamed big and was accomplishing those dreams, one after another. He was one of those people that brightened your day. I always say to try and be a light, and he truly was a light in this world.
"We will all miss him dearly. Once again, we find out that life is so fragile. The world will be a sadder and lonelier place without Mike Sadler in it. May he rest in peace."
Big Ten commissioner Jim Delany expressed his condolences to those affected by the punters' deaths in a statement Monday.
"While we are deeply saddened by their untimely loss, we also recognize the impact they had and the success they achieved as students, athletes, citizens and representatives of their respective communities and institutions," Delany said. "On behalf of the Big Ten, we greatly appreciate the enduring contributions made by these two young men, and our hearts go out to their families during this difficult time."
Foltz, 22, punted for Nebraska the past three seasons. He won the Big Ten's punter of the year award last fall and was on the Ray Guy Award watch list for the best punter in the country this summer. He averaged 44.2 yards per punt last season and had 50 career punts of 50 yards or longer.
Riley said he felt thankful to coach Foltz for one year. The coach had looked forward to Foltz's senior season in 2016 and to "watching him [go] on to play forever because he would have."
"I've had three or four punters make it to the NFL," Riley said, "and this guy was really good."
Foltz won Nebraska's Student-Athlete HERO Leadership Award in 2016 and was a four-time member of the university's scholar-athlete honor roll.
"Our prayers of love and support go out to Sam's family during this difficult time, and we will do all that we can to help comfort them in this time of sadness," Nebraska athletic director Shawn Eichorst said in a statement. "Sam was truly a tremendous young man who represented everything that a Nebraska student, athlete, teammate and friend should strive to be. While his loss is devastating, his impact will be felt forever. Along with Coach Riley, our focus is on providing Sam's family, teammates and friends with the critical support and love that they need at this time."
Foltz, a former walk-on, epitomized the spirit of Nebraska football, according to Riley, from his small-town roots to achievements at a high level.
"That's him," Riley said. "He's proud. He was really proud of it. He was really proud of being a Nebraska football player.
"I told our team he just proved to me why it's so much fun to coach because he was a really, really fun guy to be around. [He was] very uniquely special in how he approached what he did and so good at it and loved it and did it all with enthusiasm."
LSU coach Les Miles said in a statement, "Our thoughts and prayers go out to the families of Sam Foltz and Mike Sadler. We grieve for them. This isn't supposed to happen to young people who have so much to live for. We are so thankful that Colby will be able to return home to his family and friends."
Sadler, 24, was a four-year starter at Michigan State from 2011 to 2014. He finished his career ranked second in school history in punts, punting yards and punting average. Sadler was a 2013 Ray Guy Award semifinalist and earned first-team All-America honors that season.
He was the first Spartan in school history to earn Academic All-America honors four times, and he was named to the 2014 National Football Foundation Scholar-Athlete Class. Sadler intended to attend Stanford Law School this fall.
Information from ESPN's Dan Murphy, David Ching, Mitch Sherman and Jesse Temple contributed to this report.