EAST RUTHERFORD, N.J. -- Defensive coordinator Perry Fewell did the math, and the final result wasn't pretty.
By Fewell's calculations, the New York Giants' secondary allowed seven plays of at least 18 yards this past Sunday. And Fewell said he believes at least five of those plays were avoidable.
"There were mental errors or communication errors where we let people run free, when we should not have let them run free," he said.
And run free they did.
Redskins quarterback Rex Grossman, who barely beat out John Beck for the starting job in Washington, torched the Giants for 305 yards and two touchdowns. After misfiring on his first four attempts, Grossman connected on 21 of his next 30, looking less like a journeyman and more like Joe Theismann.
"We just didn't do what we had to do to put a stop to them," safety Antrel Rolle said.
Just how bad did it get for the Giants and their injury-depleted, second-rate secondary?
Grossman found backup tight end Fred Davis five times for 105 yards. Davis is the Redskins' backup tight end.
"He just found a zone," safety Deon Grant said. "The quarterback saw him and delivered it to him."
Problem was, Davis wasn't the only Redskins player to find open space. Six Redskins receivers had at least 20 receiving yards. Grossman's average completion went for 14.5 yards.
"Every now and then somebody had a little brain fart," safety Kenny Phillips said. "And every time we did, unfortunately they'd take advantage of it."
Added Grant: "They were just basic things. We can't let that happen again."
The Giants sacked Grossman four times, but Fewell pointed out that Grossman had extra time in the pocket without consistent pressure from the injured Tuck and Umenyiora. That was particularly true when the Giants were in a zone, which they played in for about half of the snaps against the Redskins.
"We consider Justin Tuck and Osi apart of our secondary," Fewell said. "That was a little bit of a problem."
Fewell said he believes most of the problems you saw this past Sunday were solved during practice this week.
But he won't know for sure until the Giants step on the field Monday against banged-up Sam Bradford and a St. Louis Rams team without one of its top receivers and, possibly, its starting running back.
Of course, the Giants will have injury issues of their own. Tuck and wide receiver Hakeem Nicks are questionable, and Umenyiora is out.
No matter who suits up, though, Fewell said he expects his defensive backfield -- arguably the most veteran unit on his injury-ravaged defense -- to step up.
"I expect more out of those guys, no question," he said.
He expects it, and he'll need it Monday night.
Ian Begley is a regular contributor to ESPNNewYork.com.