This has been building for weeks. It became clearer with every poor throw and head-scratching decision. The only question was whether Washington Redskins Coach Mike Shanahan would eventually make a quarterback change, because Rex Grossman hasn’t been very good.

On Sunday, Grossman left Shanahan no choice. The necessary move was obvious, and Shanahan made it, benching Grossman, whose awful four-interception performance was the biggest factor in the Redskins’ 20-13 loss to the Philadelphia Eagles.

After Grossman completed his third pass to Eagles safety Kurt Coleman late in the third quarter, Shanahan turned to backup John Beck to begin the fourth, and Beck provided something of a spark with his passing and running. Now, Shanahan is faced with a situation he had hoped to avoid, having yanked Grossman in favor of Beck early in the season and needing to decide whom to start next week. And again, it seems Shanahan has no choice but to give Beck a longer look.

Sticking with Grossman for the entire season was the right move, as long as he didn’t hurt the team, I wrote when Shanahan chose him over Beck. I advocated that Beck start, believing his athleticism could help Washington, and we had seen enough of Grossman last season and during his time with Chicago to have serious doubts about the Redskins succeeding with him.

Changing quarterbacks during a season, though, is among the quickest ways to derail a team. With the game’s most important position, it’s best for coaches to make a decision and go with it. Don’t look back — unless a quarterback’s play demoralizes the team.

“Everybody knows that if you have four picks in a game,” Shanahan said, “good things aren’t going to happen.”

Although Grossman sank to a new low — at least during his brief Redskins tenure — in this showcase NFC East matchup, he also was, well, Rex Grossmantoo often in Washington’s first four games.

He floated many passes that could have resulted in interceptions. He committed some of the same inexplicable turnovers that have marked his career. Bottom line, the Redskins won three of their first four, and that’s what matters most. But when the potential for disaster actually happens during a game in which Washington could have made another strong statement in the division, then something significant needs to be done. Benching Grossman for the final quarter was a move in the right direction — but it was only a start.

Reality is, Grossman needs a perfect environment, or nearly perfect, to function as a serviceable quarterback in this league. Because of injuries, Washington’s offensive line could be in shambles for a long stretch, and Grossman isn’t physically talented enough to overcome that major problem.

Not that Beck is definitely some Redskins savior either. Remember, he lost to Grossman in the preseason quarterback competition. He wasn’t good enough to finish first in a two-man race against a failed starter. Beck, though, is much more athletic than Grossman, which he displayed while working in relief against the Eagles. If Beck protects the ball better than Grossman, regardless of whatever else he does, the Redskins would be better off.

For the season, Grossman has nine interceptions and only six touchdown passes. He also has lost two fumbles. That’s 11 turnovers in five games. That’s unacceptable. “Ultimately, I’m responsible for the football,” Grossman said.

True. It was also Grossman’s responsibility to help the Redskins, even if only by not throwing interceptions, in the third quarter with Washington’s defense playing well and the Eagles’ offense, after dominating throughout the first half, slowing down.

Trailing by 14 points in the quarter, Washington’s offense had opportunities. Repeatedly, Grossman ended them. At the Philadelphia 20-yard line with about 7 minutes remaining in the third, Coleman intercepted Grossman’s pass at the 5-yard line.

On Philadelphia’s next possession, it failed on downs at the Washington 32. Three passes later, Coleman completed his three-interception day. In a span of four passes, Grossman completed two to the Eagles and none to the Redskins.

“Obviously, I would have liked to have finished what I started, from a competitive standpoint,” Grossman said.

“There are a lot of times where things aren’t going well, and all of a sudden things just go into place and it starts to get better. You start to click, all of a sudden, get into a rhythm. I wasn’t able to do that. They thought the best answer was to replace me.”

Offensive coordinator Kyle Shanahan’s body language told the story. Immediately after Coleman’s final pick, the younger Shanahan threw up his arms in exasperation. “You’re in,” Beck said Kyle Shanahan told him.

“We needed a spark,” Coach Mike Shanahan said. “John’s been practicing very well the last couple of weeks. And with four turnovers there, we thought it was time to give John an opportunity to show us what he could do.”

Since the season began, Beck hasn’t had any reps with the first-team offense. He has, however, arrived early and stayed late at Redskins Park, doing everything he could to prepare for the chance he received Sunday. He has remained focused during practice and games “just trying to do what I could, so if this did happen. And, you know, who knows what’ll happen next?”

The Shanahans probably do. It would seem they’ve already seen more than enough. Perhaps Beck doesn’t solve long-term questions at quarterback. It appears, though, that Grossman has already provided one answer.