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 has 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.
"Last night, we lost one of the best young men who I have ever had the honor to coach and who has ever worn the Nebraska uniform," Riley said in a statement. "Sam was universally loved and respected by everyone he touched and on whom he had a positive influence each and every day. His tragic loss is immeasurable to his family, his friends, his classmates, his teammates and his coaches and our thoughts and prayers are with all of them. The young men in our football program are hurting but I know that their strength of character and resolve will bring us together and we will honor Sam every day moving forward."
The Big Ten Network tweeted condolences to the families of Foltz and Sadler, while 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
— Mark Dantonio (@DantonioMark) July 24, 2016
— Mike Riley (@Coach_Riley) July 24, 2016
Dantonio added in a statement, in which he also expressed sympathy to the Foltz family and Nebraska as well, "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."
Foltz, 22, punted for Nebraska for each of 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.
Foltz also 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."
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 at the school in punts, punting yards and punting average. Sadler was a 2013 Ray Guy Award semifinalist and earned first-team All-America honors that same season.
He became the first Spartan in school history to earn Academic All-America honors four times and was named to the 2014 National Football Foundation Scholar-Athlete Class.
Sadler had intended to attend Stanford Law School this fall.
Information from ESPN's Dan Murphy, David Ching and Jesse Temple contributed to this report.