Beck was anointed as the new No. 1 on Wednesday, chosen by coach Mike Shanahan to start Sunday's game against the Carolina Panthers. Grossman gets the demotion after throwing four interceptions in a 20-13 loss to Philadelphia.
"You can't constantly turn the football over," Shanahan said. "And if you do, you're going to lose your opportunity to lead the football team."
Beck, the 30-year-old former second-round pick, will make his first NFL start since 2007, when he was a rookie for a Miami team that went 1-15. He played the fourth quarter against the Eagles after Grossman was benched, leading the Redskins' only touchdown drive of the game.
"There's been a lot of hard work that's gone into this," Beck said. "You never know when your opportunity's going to come, and you've always got to stay ready. I've tried to do that."
Beck and Grossman took turns at the podium expressing their respective excitement and disappointment, reversing their roles from six weeks ago when Grossman won the job at the end of training camp.
"Things change," Beck said, "in the blink of an eye."
Shanahan called the quarterbacks into his office Tuesday to inform them of the switch.
"I was frustrated," Grossman said. "Not completely surprised, but I'm disappointed that I wasn't able to come back off that game."
Although the Redskins (3-2) have a winning record, Grossman hasn't been able to shake reputation as a turnover machine. His nine interceptions tie him for the NFL lead with Carolina's Cam Newton, who has 42 more attempts.
Grossman has 11 total turnovers -- including two fumbles -- through five games this season, and 18 in eight Redskins starts dating to last season. He has 46 touchdown passes and 49 interceptions in a career that reached its peak when he led Chicago to the Super Bowl after the 2006 season.
Grossman's quarterback rating is 66.5, ranking 32nd of 33 quarterbacks in the league. He's ahead of Indianapolis' Kerry Collins, who hasn't played since Week 3.
Yet Grossman on Wednesday repeatedly defended his body of work leading up to the Philadelphia game.
"The frustrating part about it is I do think that they were good performances. The frustrating part is they should have been great," he said. "I had an opportunity to make it clear as day, and it wasn't. For the first four games, I played well. And I could show you to prove it, but it doesn't matter."
Grossman admitted he had an "unacceptable performance" against the Eagles and that he perhaps need to change his mind-set when it comes to turnovers.
"The only thing I could do that could maybe encompass all turnovers -- just have a little more conservative approach to the fact that, hey, turnovers are bad, but they're emotional mistakes that create emotion in the stands, create an odd emotion everywhere," Grossman said.
"Ultimately," he said, "I'm responsible for the ball."
Beck is also more agile than Grossman, an important advantage given that the Redskins lost two offensive line starters to injuries against the Eagles.
"I have a lot of confidence in John Beck because he does have that mobility, that strong arm," Shanahan said. "I'm not going to be putting him in the Hall of Fame yet, but I really do believe he's got a lot of talent."
Beck becomes the 21st quarterback to start a game for Redskins in 19 seasons, reflective of the franchise's overall lack of stability. He will be the third starter in 22 games under Shanahan, who whiffed last year with Donovan McNabb and said at the beginning of the season that he would stake his reputation on both Grossman and Beck.
"We don't mind going to bat, taking a shot at a guy that was very talented," Shanahan said. "I watched Donovan through the years. ... We brought him in here to see if it would work out. It didn't work out. ... There's nothing wrong with admitting you made a mistake or that guy's not the future of your organization."
"You've got to see what's out there," the coach added. "It's not like they fall out of trees."
Beck said he's improved since training camp, having learned more about the offense as the No. 2, making up for study time lost during the NFL lockout. He completed 8 of 15 passes for 117 yards in relief against the Eagles and scored on a 2-yard run.
That gave him a modest QB rating of 79.0 -- much better than in any of his five games with the Dolphins. He went 0-4 as a starter in 2007 and made one relief appearance for a bad team.
He's been waiting for another chance ever since.
"The situation I stepped into as a rookie was a very difficult one because we were winless, the organization had been through a lot of struggles that year," Beck said. "We were already 0-9. This is still the beginning part (of this season), and this team has a good feel about it."