SANTA CLARA -- Eric Mangini's mantra when it comes to the 49ers defense: flexibility.
"Sometimes that’s just a catch phrase," Mangini told SI's MMQB this week, "but I grew up that way defensively, and I believe in that, where each week we are going to have challenges we have to deal with, and we have to have the tools and flexibility both physically and mentally to get that done in a very short time frame. So I’m a big believer in building flexibility into the defense, too."
That flexibility could be seen in the 49ers' recent practices. A young cornerback like Keith Reaser, for example, might have lined up at on the left, outside with the second-team defense one day, the nickel spot with the first-team defense the next and at right cornerback the following week.
That was partially to figure out where Mangini's talent lies -- he has a slew of young cornerbacks who don't have a lot of playing experience, and he must learn where each player fits best. The offensive coaches also mixed and matched extensively in May and June, especially on the offensive line.
"Coach has been throwing us around," cornerback Kenneth Acker said. "So ... you're not going to play in the same position, not play the same side. Some people are inside, some people are outside, some people are at safety. I think we've got a lot of different guys that can do a lot of different things. And coach sees that. He's feeling us out just like we're feeling the positions out."
But there's also a sense that the 49ers will be chameleon-like on defense this year, changing shapes -- and personnel -- to match their opponent. The team's lineup when speedy, shifty Giants receiver Victor Cruz is in the slot position on Oct. 11, for instance, could be different than what it will be two weeks later when towering Seahawks tight end Jimmy Graham is in the slot.
Jimmie Ward and Dontae Johnson both played the nickel position last season. At 6-2, Johnson is a possibility when it comes to covering Graham, who stands 6-7. So is second-round draft pick Jaquiski Tartt, who at 6-1, 221 is the bulkiest of the 49ers' defensive backs.
With Ward out with a foot injury this spring, Leon McFadden, Reaser and Tramaine Brock spent time at nickel. Reaser is perhaps the 49ers' fastest cornerback, and he played some nickel at Florida Atlantic University.
Brock, meanwhile, is the team's top cornerback, and there has been talk that he will follow the opponent's best wide receiver all over the field. He may also follow if that receiver moves inside to the slot position.
Other cornerback notes ...
You may remember a story a few years ago about how Jim Harbaugh and the 49ers took their practice squad players on the road with them, which isn't something every team does. The same goes for players who are on injury lists.
Those players not only go on the road with the team, they go to meetings as if they were perfectly healthy and playing, and they get fined if they show up late, fall asleep in a meeting, and so on and so forth.
"The only thing we didn't do last year was touch the field," said Acker, who dealt with a foot injury last year.
As a result, Acker said, he doesn't feel like a rookie, despite the fact that he didn't suit up for any regular season games a year ago. The pregame routine of going to an opposing stadium -- Seattle, for example -- will be old hat to him because he did it eight times last season.
"We really didn't feel left out in any way," he said. "We knew that our time would come. And now it's here."
General manager Trent Baalke has likened, on more than one occasion, incoming 49ers cornerback Shareece Wright to former 49ers cornerback Carlos Rogers. That's partly due to their styles of play. And it's partly because of their similar story lines.
Before Rogers arrived in San Francisco in 2011, he was considered a disappointment with Washington. He was a former first-round pick who was short on big plays, especially interceptions. In his first year with the 49ers, however, he had six interceptions, was the de facto captain of the secondary and went to the Pro Bowl.
Is Baalke predicting a Pro Bowl season for Wright? No. But his point is that, like Rogers, Wright is not nearly as bad as people perceive him to be and that a good front seven will benefit a veteran like Wright just like it did Rogers in 2011.
Reaser missed 2014 with an ACL issue. Asked if his speed has returned in full, the former track star said, "I haven't run a 40 (yard dash), so I don't know an exact time. But I feel good. I feel like my speed's there, the explosion. Just working off some rust, (working on) technique."
The 49ers coaches and team officials will say that they're excited about all of their young cornerbacks. Reaser, however, is perhaps the apple of their collective eye.