Back off. Smith, who abruptly walked away from the Minnesota Vikings after the 2000 season, said he understands why Williams quit the Miami Dolphins last week, less than a week before the start of training camp. He said Williams, a running back like Smith, made the right decision — even if Williams was in his playing prime and the peak earning years.

“For his mental and physical health, it was best,” Smith said. “Playing football is not something you can do 80 percent mentally. It didn’t make sense to keep going.”

Williams became the latest in a string of athletes who caught their sport, their team, their fans by surprise. They are rebels and nonconformists willing to walk away from adulation and millions of dollars to do something else — or nothing else.

Slugger Ken Harrelson left major league baseball in 1971 to take a shot at the PGA Tour. He failed. Superstar Michael Jordan walked away from the NBA to try to play baseball. He struck out. Safety Pat Tillman shunned a multimillion-dollar contract from the Arizona Cardinals to join the special forces. He died in an Afghanistan firefight. Defensive tackle Mike Reid left the Bengals in 1974 at 26 to play the piano. He has since written 10 No. 1 country music hits and has two Grammy Awards.

Smith quit an NFL career and has been laying low since.

Some share a different world view than most, one that clashes with America’s sports-crazed culture. Others simply burn out. But fans, who live vicariously through their sports heroes, feel betrayed.

Smith said his perspective changed when he was a freshman at Ohio State. Before a game against the University of Michigan, Bill Miles, then the OSU offensive line coach, caught him looking nervous. He pulled him aside and said, “Robert, this game is important. But there are a billion people in China who don’t even know this game is going on.”

Said Smith: “That changed things. If you just turn on your TV and listen, there are lots of important things happening in the world. Don’t always put on SportsCenter.”

As a running back with the Vikings, Smith, on Tuesdays, visited children suffering from cancer. He heard their stories, met with their parents and followed their struggles. Then, on Wednesdays, he would answer questions about the upcoming game’s importance. The contrast disturbed him, he said.

When Smith retired, he faced much of the same criticism as Williams. Although Smith had talked about nobler pursuits throughout his career, few suspected he would quit at age 29 after rushing for 1,521 yards in 2000, his best season.

“For someone like me or Ricky, there are just more important things in life,” Smith said. “Everyone was talking to me like, ‘This is a do-or-die game this week.’ Well, I had just spent the day before with a 6-year-old dying of cancer. It just didn’t jive.”

Williams and Smith spoke in June while working together at a camp. Smith talked to Williams about his upcoming book, “The Rest of the Iceberg,” which will articulate Smith’s position on sports in American society and the life of a professional athlete. During their conversation, Williams — painfully shy and suffering from social anxiety disorder, hinted he was considering retirement.

Smith said Williams had mulled the decision for months. He told the Dolphins a couple of days before camp opened because that’s when he arrived at his decision, Smith said. But with their offense built around Williams, a powerful runner, the Dolphins were left with few options for replacing him.

“There’s no question he could have picked a better time,” Smith said. “But it wasn’t like this was an overnight decision, and he decided a week before training camp just to (hurt) them.”

Williams left reportedly facing a drug suspension, and he told the Miami Herald his desire to continue smoking marijuana contributed to his decision to quit. He also may owe the Dolphins $8 million because of his early exit.

All that aside, Smith said if teammates and fans stop and consider Williams’ decision, they will understand it.

“For the fans, look, he has real issues more important than entertaining you,” Smith said. “He doesn’t live to entertain you and make your ticket worthwhile.”

Williams and Smith are not the only NFL running backs to have bailed in the prime of their careers. In 1965, Jim Brown left the Cleveland Browns to pursue an acting career. And in 1999, with Walter Payton’s rushing record within reach, Sanders walked away from the Detroit Lions. But Sanders said he had trouble making sense of Williams’ decision.

“I’m as surprised as anyone,” Sanders told The Associated Press. “Even for me, it seems very strange.”

John Riggins, a running back who turned a holdout into a short retirement, refused to criticize Williams, too.

“He was satisfied with what he got out of it,” Riggins told the Miami Herald. “He’s walking away from the game, running away from the game, which a lot of us can’t do because we played longer than we were supposed to. I’m not overly religious, but the Bible says, ‘To thine own self be true.'”

Williams’ decision was less surprising to psychologists. Athletes burn out, they say, when they feel like they have lost control. Certain personality types, particularly free spirits like Williams, are more prone.

“Burnout often results from feeling trapped in a position,” said Dr. David Feigley, a sports psychologist at Rutgers University. “Sometimes we think of it as overwork. But if it’s overwork and you still feel in control, you’re less likely to burn out.

“Why do you go to practice? If the answer is, ‘I have to,’ as oppose to, ‘I chose to,’ you’re more prone. Burnout tends to happen when you’re working in area you once enjoyed, but now there are all these external constraints.”

That seems to apply to Williams, who said he felt “free” after announcing his retirement.

“My heart tells me, ‘Don’t be controlled,'” Williams told the Miami Herald. “Everyone wants freedom. Humans aren’t supposed to be controlled and told what to do. They’re supposed to be given direction and a path. Don’t tell me what I can and can’t do. Please.”

Dr. John F. Murray, a sports psychologist based in West Palm Beach, Fla., said teams need to be more proactive in tapping into with players’ psyches. Having a full-time sport psychologist as part of the coaching staff would be a good start, he said.

Murray said he worked with two high-profile athletes on the verge of quitting. One, he said, went on to win the Super Bowl with the New England Patriots. The other was tennis player Vince Spadea, who wanted to quit after enduring a 21-match ATP losing streak.

“There are many ways to keep people fresh and keep their desire to play sports alive,” Murray said. “We have maxed out on physical training, but we haven’t come close to realizing our potential when it comes to dealing with the mental side.

“It’s time for coaches to wake up and realize you can’t address these issues in old-fashioned, antiquated ways. It’s time to wake up and get real and help these athletes.”

In some cases, psychologists say, a break will help an athlete recover and prod him toward returning, as was the case with Jordan.

Smith admitted to missing football. But he believes there are more important things.

“Just because you can do something,” Smith said, “doesn’t mean you should.”

LEAVING SO SOON?

A look at pro athletes who retired early for reasons other than injury or illness:

Bjorn Borg: He won 11 majors, including five consecutive Wimbledons and four straight French Opens before quitting in 1981 at age 25. His comeback at 34 was short-lived.

Jim Brown: Considered the greatest running back in NFL history, he left the game at 30 to become an action-film star and civil rights leader.

Jennifer Capriati: Burnout and drug issues led her to quit at age 17 in 1993. She returned to win three Grand Slam titles, and she became the top-ranked player in the world for parts of 2001 and ’02. Now 28, she is still a top-10 player.

Dave Cowens: At 28, he quit after his friend Paul Silas was traded after the Celtics’ 1976 championship season. Cowens returned after 30 games, retired again after the 1980 season, returned in 1982, then quit again. He has coached Boston, Charlotte and Golden State.

Ken Harrelson: After hitting 65 home runs in his two previous seasons, Harrelson left the game at 30 to try to make the PGA Tour. He fell short but built a career as a baseball analyst.

Michael Jordan: He retired three times, once to play baseball. He returned to lead the Bulls to their second three-peat from 1996-98. He finished his career with two so-so seasons on the Wizards and is now looking for an NBA franchise to own.

Rocky Marciano: After going 49-0 as a pro, the heavyweight champion retired in 1956 at age 31. Unlike other champs, he never returned, and died at 45 in a plane crash.

John Riggins: He was 31 when he turned a holdout into a one-year retirement. He returned in 1981 and was the Super Bowl XVII MVP before retiring in 1986.

Barry Sanders: The Lions’ running back was within 1,500 yards of breaking Walter Payton’s career rushing record when he suddenly retired before training camp in 1999.

Robert Smith: The former Vikings running back led the NFC with 1,521 yards rushing in 2000 and walked away from a potential $40 million free-agent contract.