RENTON -- Linebacker is the single most difficult defensive position to assess in training camp.

You can see a cornerback's coverage skills or a defensive end's speed rush, but tackles are what define a linebacker, and when you take that out of the equation as teams do during practice, it's hard for an observer to draw any conclusions about who's doing what.

So let's ask a guy who's assigned to block those linebackers for an evaluation: fullback Michael Robinson.

And what he said about rookie middle linebacker Bobby Wagner was enough to make you stop and wonder if he was serious.

"He still has long arms," Robinson said. "Great, long arms. Very explosive. He's a guy that can run sideline to sideline. He's learning. He's still a young guy. He's still learning how to get off blocks in the National Football League. He's going to be another special player one day. I call him a 'Baby Patrick Willis' because I hadn't seen a linebacker move like that since Pat."

Whoa. Patrick Willis? That's the gold standard for linebackers in this division and around the league. The man has made the Pro Bowl in all five seasons since the 49ers drafted him in the first round out of Ole Miss. He's been a first-team All-Pro the previous four years.

So, really, Mike? Patrick Willis?

"Well, it's the truth," Robinson said, "and I've been against both of them."

That's true. Robinson was Willis' teammate from 2007 through 2009 in San Francisco, and now he's seeing Wagner, whom the Seahawks drafted for his speed.

"He's fast," Robinson said. "He's explosive, and again, just the way he slips blocks, and it seems like he's always going toward the ball. He's not worried about a blocker, and he's learning, obviously. He's still young, but he definitely has the ability."