Williams, who would have been a junior next season, announced his decision in a heartfelt letter on Arkansas' official website. His letter was titled "Next Chapter" and comes on the heels of a neck injury he suffered during the Razorbacks' final spring scrimmage last month. Williams had to be carted off the field and taken to the hospital.
"I've seen the replay. I saw a normal hit. That scared me," Williams wrote in his letter. "It shows me it doesn't take a big hit at this point. Any little thing can trigger it. I also saw the reaction of my mom and my sister. That broke my heart. I can't do this anymore. I want to be able to walk."
As a freshman in 2015, Williams suffered the first neck injury in a game against Auburn and underwent surgery to fuse a disk in his neck.
"I'm moving onto the next chapter of my life," Williams wrote. "It's tough to not be able to play football anymore because I've been playing since I was four years old. It wasn't something I wanted to do or planned on having to do so early. I've prayed, listened to my doctors, my parents and my gut.
"It still doesn't seem real yet, but I really don't have a choice. I've dodged the bullet twice. I realize at the end of the day I want to live a normal life and be around my family."
"I've seen the replay. I saw a normal hit. That scared me. It shows me it doesn't take a big hit at this point. Any little thing can trigger it. I also saw the reaction of my mom and my sister. That broke my heart. I can't do this anymore. I want to be able to walk." Rawleigh Williams III
Williams, 20, and his family met with doctors and Arkansas coach Bret Bielema last week before he made his final decision to walk away from football. He will be a student assistant for the football team in 2017.
"Coach B [Bielema] has been someone I've looked up to since the day I met him," Williams wrote. "He's always been there for me. I'm grateful to him for the opportunity to play football at the University of Arkansas and in front of the best fans in college football. I'm grateful for the opportunities I'm going to earn during the rest of my time here. I can't wait to work under him and learn. I want to be a general manager one day, and he's already helped me look into career paths to achieve my goals."
Williams led the SEC with 1,326 rushing yards at the end of the regular season. LSU running back Derrius Guice and Mississippi State quarterback Nick Fitzgerald moved past Williams with strong performances in bowl games. Only 27 yards separated the three players.
"At Arkansas, not only does he have All-SEC academic success, but he also steps away as the reigning SEC regular season rushing leader," Bielema said in a news release. "This next chapter in Rawleigh's life will be filled with unlimited success in any career path or anyway of life he chooses. As a head coach I couldn't be more excited to begin the next chapter with him and be there for him."