Chicago Bears defensive coordinator Ron Rivera is no doubt thrilled that his defense held the high-powered New Orleans Saints to 14 points in the NFC Championship Game, sending the Bears to the Super Bowl. But it would be hard to blame Rivera if a part of him wonders whether his stellar game plan against the Saints actually damaged his own career prospects.

NFL rules put assistant coaches on Super Bowl teams at a decided disadvantage when they try to become head coaches elsewhere. The league limits assistants to one brief interview while their teams are in the playoffs, but assistants on teams that have been eliminated can interview all they want. At first glance, the rule might seem to make sense: It frees assistants whose seasons have ended to pursue advancement in their coaching careers and puts the top priority of assistant coaches whose teams are still in the playoffs where it should be, on helping their own teams rather than trying to impress the owners with coaching vacancies.

But while the rule sounds good in theory, it doesn’t work in practice. Rivera, who like most assistants aspires to become a head coach, was placed in an awkward position when the Arizona Cardinals and Pittsburgh Steelers expressed interest in his services for their head-coaching jobs. Rivera met with both teams for interviews in the week after the regular season ended, meaning he couldn’t give his full attention to the Bears as they began preparations for the playoffs. But the league’s rules prevented him from returning for a second interview, meaning the other candidates for those jobs could gain a competitive advantage by spending more time with the Cardinals’ and Steelers’ owners.

As it turned out, the Cardinals and Steelers both bypassed Rivera to hire assistant coaches from teams that weren’t in the playoffs. NFL coaching searches usually work out that way: In the last 10 years, only one assistant coach on a team that played in the Super Bowl became the head coach of another team that year: Romeo Crennel, who was named the Browns’ head coach two years ago after coordinating the New England Patriots’ defense in the Super Bowl. Several other qualified assistants have been passed over for head-coaching jobs because teams looking for a new head coach don’t want to wait until after the Super Bowl to find him.

Before Crennel, the last time an assistant on a Super Bowl team became a head coach elsewhere was 1995, when two assistants from the Super Bowl champion San Francisco 49ers became head coaches for the first time: Ray Rhodes, who was hired by the Philadelphia Eagles, and Mike Shanahan, who was hired by the Denver Broncos. In 2000, the NFL’s two hot assistants were John Fox, the Giants’ defensive coordinator, and Marvin Lewis, the Baltimore Ravens’ defensive coordinator. The Giants and Ravens met in the Super Bowl at the end of that season, which should have showcased each assistant’s potential to become a head coach. But neither Fox nor Lewis snagged a head coaching job – by the time they were free to interview, all the job openings had been filled.

Fox became head coach of the Carolina Panthers a year later, when the Giants missed the playoffs and gave him all of January to focus on job interviews. Lewis moved on to defensive coordinator of the Washington Redskins and then became head coach of the Cincinnati Bengals after the 2002 season, when, like Fox a year earlier, he had no restrictions on his interviews because the Redskins missed the playoffs.

This off-season has had six headcoaching vacancies, and none of the teams looking for new coaches seem willing to wait for an assistant with the Bears or the Indianapolis Colts. In addition to the Cardinals and the Steelers, who declined to wait for Rivera, the Miami Dolphins hired San Diego Chargers offensive coordinator Cam Cameron, moving quickly after the Chargers lost their first playoff game. The Atlanta Falcons and the Oakland Raiders both filled their head-coaching vacancies with college coaches who aren’t constrained by the NFL’s rules on assistants. The Dallas Cowboys job is still open after Bill Parcells retired last week, but Dallas owner Jerry Jones has already begun interviewing candidates and may make his final decision this week, before any assistants on the Bears or Colts staffs would have a chance to apply for the job.

The NFL should level the playing field for assistants by changing its rules. The league should implement a hiring freeze, saying no team can interview head-coaching candidates until after the Super Bowl. Free agent players can’t begin to negotiate new contracts immediately after the season ends, and assistant coaches shouldn’t be allowed to, either. Although some teams would object, saying they need to hire new coaches early in January to begin the process of hiring a staff and preparing for the draft, as long as the rule applies to every team, it won’t put any team at a competitive disadvantage.

Rivera’s inability to land a headcoaching job isn’t for lack of credentials. He was a linebacker on the great 1985 Bears defense that won the Super Bowl, and as an assistant he has worked with two of the league’s best defensive coaches, both in his current job under Bears head coach Lovie Smith and previously as the linebackers coach for Eagles defensive coordinator Jim Johnson. Rivera has all the qualifications to be a head coach. Someday he will be — just as soon as his defense stops leading the Bears into the Super Bowl.

Mr. Smith is a writer for FootballOutsiders.com.