Washington Redskins coach Mike Shanahan said Rex Grossman’s turnover-prone play, the way John Beck handled himself in a pressure-packed situation Sunday and the backup’s mobility all factored heavily in his decision to give Beck the starting quarterback job.

Grossman threw four interceptions in three quarters against the Eagles Sunday, increasing his turnover total in eight games as Washington’s starter to 18. Beck entered the game in the fourth quarter and completed eight of 15 passes for 117 yards and rushed for a touchdown.

“I thought John did a good job with three of our starters out in the fourth quarter against Philly to come in in a situation where they knew we had to throw the football, get nine first downs--could’ve attempted a field goal on the one, took us down the field, 75-yard drive for a touchdown – impressed with that. Put a lot of pressure on him in that situation. I like the way he’s been practicing the last few weeks. He’s done a good job in practice. I think he deserves the opportunity for us to see what he can do.”

Grossman beat out Beck during the preseason, but after his nine interceptions, two fumbles and only six touchdown passes in the first five games, Shanahan felt like the Redskins needed to go in a different direction.

“I said, ‘Hey, to keep that position, quarterback in the National Football League, you have to eliminate those mistakes.’” Shanahan said of his conversation with Grossman. “Like we talked about the Giants game, there’s always going to be mistakes made in the game, but you can’t constantly turn the football over, and if you do, you’re going to lose your opportunity to lead the football team.”

Now, can Beck do better?

Shanahan said that based on what he has seen from Beck in practices and in Sunday’s game, he believes the quarterback is more comfortable in the system than he was during the preseason. And he believes Beck’s mobility will serve him well.

“There’s always factors involved, but I think a big plus for John is his mobility. He’s a 4.7 [second, 40-yard-dash] guy. He can make plays with his feet. He has a good command for the offense. I think he feels more comfortable with it now than he has since he’s been here. So now he’s going to get his chance.”

Asked whether Beck could be the long-term solution at quarterback, Shanahan said, “I don’t think there’s any question about it.” He didn’t say how long a leash Beck will have, but added that Beck needs to prove himself continually.

Shanahan now is on his third quarterback since coming to Washington in April of 2010. He traded Jason Campbell before the Auburn product ever went through a practice with him and traded for Donovan McNabb, whom he compared to John Elway when he was introduced. Now McNabb is gone, and Shanahan has sent Grossman to the bench. An unproven quarterback now is at the helm.

When asked if he feels more pressure now that he his first two quarterbacks have failed, Shanahan said this is just part of the job.

“The first year when I came here, I had to make the decision with Jason Campbell or Donovan McNabb,” Shanahan said. “And I went with Donovan. I took a shot. There wasn’t a whole lot out there at that time. There were a lot of decisions to be made. Obviously, that didn’t work out, but I wasn’t going to keep him here for three or four years. You make a decision if he’s the guy for the future and he wasn’t, so we went with Rex and obviously we have John Beck as well. We’ll see how these guys do. I have a lot of confidence in them, but we have to play well. It’s not just your quarterback — it’s your whole unit playing well together.”

Perhaps for the first time, Shanahan admitted that he made a mistake in trading for McNabb. But, in a long explanation, Shanahan said that he’ll keep on swinging until he finally hits a home run at quarterback.

“Let’s talk about Donovan to start out with. 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. One of the things I thought made Donovan was his great arm strength, [and] his ability to make plays running the football. We brought him in here to see if it would work out. It didn’t work out. We gave up a second-round draft choice. For Jason Campbell, we got a fourth in return, so it was really a second and a fourth, but releasing Jason and bringing [McNabb]down here, we gave up a second.

“We moved from 10th to 16th so we got our No. 2 [pick] back. But we made a decision after we were done — hey, it didn’t work out. There’s nothing wrong with admitting you made a mistake or that a guy’s not your future of the organization. The mistake I think you make is when you try to justify something you did and you don’t believe it’s going to work out. We’re going to play — at least from my opinion — the guys that are going to work out, guys we feel that are hungry, guys that are going to take us to the next level. We’re going to constantly stay with those guys, regardless. If it’s a [draft pick], if it’s a free agent — I’m very happy with our free agents this year. We brought a free agent in here that didn’t work out, even if we did pay him a lot of money. [He’s] not going to be with our football team. I believe that’s why you build a great organization. Are we going to make mistakes? Sure we are. But those mistakes, obviously, we’ll try to go through the little things so we can eliminate them. But we will make them from time-to-time.”