Ben Roethlisberger led one final drive for the Pittsburgh Steelers on Sunday night in a game that was over before it had officially ended, the same as his N.F.L. career.

Roethlisberger, who will turn 40 in March, has all but announced his retirement after 18 seasons as the Steelers quarterback. Following his team’s wild-card round playoff loss to the Kansas City Chiefs, Roethlisberger spoke at a news conference about moving “from one chapter to the next.” He said that he hugged Cameron Heyward, the next longest-tenured Steelers player, and told him that the figurative torch was now his.

“It will probably really hit me come training camp time,” Roethlisberger said.

The 42-21 loss, Roethlisberger’s worst playoff defeat, abruptly ended a Steelers season that had perhaps gone on too long. His goodbye tour began two weeks earlier, when Roethlisberger acknowledged before a final home game in Pittsburgh that “this could be it.” His team sneaked into the postseason as the A.F.C.’s No. 7 seed but was no match for Kansas City, the conference’s new superpower.

Despite the game’s wide margin, the Steelers called their last timeout with 11 seconds left, giving Roethlisberger one more chance to exit on a touchdown.

The element of time is prominent in Roethlisberger’s career. He won a Super Bowl in his second N.F.L. season, and added another championship ring just three years later, achievements that are expected to earn him a spot in the Pro Football Hall of Fame. He collected 165 regular-season wins as a starting quarterback, fifth most in league history, and sits in the top 10 in the major career passing categories.

But as time has worn on, he has become less able to deliver the style of play that earned him those early successes: Tough and instinctual backyard football, predicated on his ability to absorb hits and extend plays beyond reason. His 6-foot-5, 240-pound frame, which once required multiple defenders to tackle, became worn down through the accumulation of contact, injuries and age.

During his peak, Roethlisberger’s success obscured two allegations of sexual assault made against him. A hotel employee in Lake Tahoe, Nev., filed a civil suit in 2009 saying that Roethlisberger had raped her in his hotel room. Then, in March 2010, a college student in Georgia told police that Roethlisberger had sexually assaulted her in a nightclub bathroom, while her friends said that they were blocked from reaching her by two off-duty Pennsylvania police officers who had accompanied Roethlisberger that night. Roethlisberger denied both accounts.

He later settled the lawsuit in Nevada, and the local district attorney in Georgia declined to pursue criminal charges, citing a lack of evidence. The student had also requested not to press charges; her lawyer wrote a letter to the district attorney that said that she did not recant her account, but that her participation in a trial that was expected to have “extraordinary media attention” would be personally intrusive.

There were questions about the handling of the Georgia case. The restroom where the assault was said to have occurred was cleaned the next day, potentially destroying evidence, and the police officer who initially investigated her case later referred to the woman with an expletive.

After the police investigation, the N.F.L. suspended Roethlisberger for the first six games of the 2010 season, the first player to be suspended under the league’s personal conduct policy without having been charged with a crime. The penalty was later reduced to four games. That season, Roethlisberger led the Steelers back to the Super Bowl, where they lost to the Green Bay Packers.

Both allegations made against him came years before the N.F.L. sought to strengthen its response to allegations of sexual assault and partner violence, and before the #MeToo movement brought attention to accounts of assault and harassment. It is impossible to know if different timing would have changed how the cases against Roethlisberger were handled — either legally, by the N.F.L. or by sports media — only that those who consider his legacy now do so in a very different climate.

Roethlisberger’s hint at retirement resulted in his receiving a home send-off at Heinz Field in Week 17 against the Browns, a win that kept alive the limping Steelers’ playoff chances. Thomas Tull, a minority owner of the team, took out a full front page ad in the Sunday edition of The Pittsburgh Post-Gazette thanking the quarterback, and Roethlisberger did a postgame lap around the stadium to salute fans. His wife, whom he married in 2011, and their three children met him in the tunnel afterward.

During the “Monday Night Football” broadcast, ESPN color commentator Brian Griese made a reductive reference to Roethlisberger’s being “immature” and having made “mistakes” early on, adding that the fan base “forgave” him. This effort to sanitize his farewell was, at best, an oversimplification. There is no easy way to juxtapose two sexual assault allegations with the 18 years Roethlisberger bolstered the Steelers with his play, but both are part of his N.F.L. career.

A person’s legacy isn’t always neat and tidy, and the same goes for endings. With one play left in Kansas City, Roethlisberger completed his last pass, but his target, tight end Zach Gentry, was tackled short of the end zone. The Steelers could no longer stop the clock, and the final seconds ticked away.