Signing Matt Forte has proven more difficult than tackling him.
Forte's value has been as a moving target, shifting left, cutting right and then spinning away.
That's why, with five months remaining until his contract expires, he remains unsigned and there has been no recent movement.
If the Bears judged Forte solely on what he was before this season, they probably would have considered him a good running back, but not an "elite" back.
He came into this year averaging 3.9 yards per carry. Of active backs, 54 had a better number. Six backs had more rushing yards between 2008 and 2010.
But Forte's value to his team isn't just as a taker of handoffs. His 4,731 scrimmage yards were fifth most in the NFL among running backs in his first three years.
He also accounted for 33 percent of his team's offense over that period. Only one player -- Chris Johnson of the Titans -- accounted for a greater percentage.
This is attributable to a number of factors. Talent, obviously. Durability. Versatility. Offensive design. And, to a degree, the paucity of productive teammates.
But the point is Forte was pretty valuable to the Bears for the first three years of his career. And he has become more so this season.
Forte is just getting to the sweet spot of his career as it is common for running backs to begin to peak in their third and fourth seasons.
In the offseason before 2010, Forte figured out how to maximize his speed with specialized training. This July, he came to camp looking as muscled up as one of those Under Armor dummies. And he has found the perfect offensive system for his abilities.
This year, Forte leads the NFL in scrimmage yards from a running back with 158.5 yards per game. If he can do that for 16 games, he will have the third most productive season for a running back in history, behind only Priest Holmes (163.4 in 2002) and O.J. Simpson (160.2 in 1975).
That could make him the best bargain in football with a 2011 salary of $555,000.
You don't want to overreact to four games of evidence, but Forte compares pretty well to other active backs. After the Vikings' Adrian Peterson and Titans' Chris Johnson, you can make a case that Forte is as valued a commodity as any of them.
I would put him on that next tier along with the Ravens' Ray Rice and Jaguars' Maurice Jones-Drew.
He has been more durable than rushing leader Darren McFadden. He has less wear and tear on him than Steven Jackson and Frank Gore. He is healthier than Jamaal Charles.
He is more versatile than Michael Turner. He is more stable than Cedric Benson. He has a bigger body of work than Peyton Hillis and Arian Foster. He has been productive more consistently than DeAngelo Williams. He's better between the tackles than LeSean McCoy.
Where does that place him on the pay scale? Below Peterson and Johnson, whose new deals average $14.2 million and $13.5 million per year annually. He's probably somewhere in the vicinity of Jackson, Williams and Jones Drew.
The new contracts of Jackson and Williams average $8.6 million. Jones Drew's new deal averages $7.6 million.
The truth is Forte was an average runner his first two NFL seasons. He was a significantly better back last year, and he's better still this year. The average per carry for his first 574 runs (pre-2010) was 3.8.
Over his last nine games, going back to last December, he has averaged 5.0 yards per carry, 85 rushing yards per game and 149 total yards per game.
It probably isn't realistic to think Forte can continue to improve as he has, but his arrow is pointing up. He is 25. Assuming most running backs start to wear down around 29, he should have four strong seasons left before he needs to be reevaluated.
Forte should be paid not for what he might develop into, or for what he has been, but for what he is now.
It's really not a bad thing to have Forte unsigned. The Bears always can hit him with a franchise tag if they need to, though that is not the optimum solution.
But having him unsigned keeps a giant carrot over his helmet, and it also continues to bring clarity to what he truly is worth.