SANTA CLARA If you ask Vic Fangio, he'll tell you the term "nickel cornerback" is a bit of a misnomer.
Sure, the person who plays the position has to be cat-quick and must be excellent in coverage. But he also has to be able to make plays around the line of scrimmage like a linebacker, which is typically the position the nickel player replaces.
"His responsibilities are linebacker responsibilities, so there's no carryover, mentally, from the corner position to the nickel position," the 49ers' defensive coordinator said Saturday. "They are two separate positions mentally."
Fangio has one excellent option in Carlos Rogers, whose six interceptions tied for the team lead last season and who was voted to his first Pro Bowl.
Rogers typically started games at left cornerback but moved inside to nickel when opponents used three wide receivers.
Fangio's goal during training camp is to develop a few others.
The position has become a critical chess piece for defensive coordinators who must counter offenses that regularly use three or more wide receivers.
When the 49ers defenders take the field for the season opener Sept. 9 in Green Bay, for example, they are more likely to be in their nickel package than they are their base defense.
Fangio also noted the 49ers use two nickel backs when opponents trot out four wide receivers. And the team's schedule this season is filled with teams that like to do just that.
The Buffalo Bills, who visit Oct. 7, used a four-wide receiver formation 333 times last season, according to Pro Football Focus, which was nearly one-third of their total plays. The Chicago Bears and Arizona Cardinals also are among the league leaders when it comes to four-receiver sets.
Other 2012 opponents such as the Packers and New Orleans Saints don't use four wide receivers as often. But both teams like to line up three wide receivers with a tight end Jermichael Finley and Jimmy Graham, respectively with wideout-like skills.
Fangio, however, has more options this season than he did a year ago.
Two newcomers, free-agent cornerback Perrish Cox and undrafted rookie safety Michael Thomas, show promise at the position and have been receiving praise from coaches since the spring.
Cox is one of the 49ers' most physical and aggressive defensive backs, and he's proven to be good at jamming receivers at the line of scrimmage.
"He's given us added depth and he's going to push for added playing time if he continues the work that he's showing so far," Fangio said in June.
Thomas, meanwhile, played the nickel role at Stanford, including in 2010 when Fangio was the team's defensive coordinator.
While a cornerback's biggest ally is the sideline, Thomas said nickel backs who play in the middle of the field don't have that sort of assistance. Instead, they have to know exactly where teammates their help are at all times, which requires a thorough understanding of the defense.
"You have to be a technician to play it," Thomas said. "That's what Carlos is good at, and it's why he had so much success last year. And that's why I'm trying to pick up as much as I can from him."
Thomas said he got a lot of training against spread offenses at the college level, especially against current teammate LaMichael James and the Oregon offense.
But he said he was still blown away by the quickness of the 49ers' slot receivers, particularly Kyle Williams and tight end Delanie Walker, who often lines up as a wide receiver.
Thomas said he was positioned opposite Walker during a recent practice and expected to encounter a powerful but lumbering tight end. Instead Walker caught an out route, turned up field and left the rookie in his dust.
"I had never played against a tight end type that was that quick and fast," Thomas said. "That was a wake-up call. Welcome to the NFL."