The free agency chants can be heard in nearly every NFL city. The consensus belief: sign Nnamdi Asomugha because he will make good things happen for the team. Fans in Philadelphia and New England hope signing him could earn championships. Meanwhile, fans in Houston and Detroit believe signing him could change franchise fortunes from chump to contender.

Nnamdi Asmougha's game-charting stats prove he's one of the league's best cornerbacks, yet the Oakland Raiders had a 85.6 defensive passer rating in 2010. In fact, since Asomugha emerged on the scene in 2006, the Oakland's best DPR was 74.1. If the Raiders couldn't build an elite defense around him in five years, can a needy defense immediately turn around their fortunes with Asomugha?
Make no mistake; Asomugha rightfully earned the reputation of being one of the league’s best cornerbacks. However, that doesn’t mean Asomugha will single-handedly improve whatever defense he joins. In fact, if statistical precedent has any say, his impact will likely be relatively minimal.
Below are five examples of all-time great cornerbacks from the Live Ball Era joining a new team, and how those additions affected the respective new teams.
Note: Each statistical line shows the net yards allowed by the defense. Net yards include sacks, which are NOT factored into passer rating or Defensive Passer Rating. The passing yards that factor into passer rating and Defensive Passer Rating are used before the sack yardage is subtracted to create the net yards.
Mike Haynes (New England Patriots 1976-82, Los Angeles Raiders 1983-89)
From his first year in New England, Haynes stood out as an elite cornerback. A nine-time Pro Bowl selection, Haynes received perhaps his highest honor when named to the NFL 75th Anniversary All-Time Team. After falling short in the strike-shortened 1982 season, the Raiders hoped to use that type of a talent for a Super Bowl run in 1983. After the Raiders landed Haynes in a trade with the Patriots, they went on to win Super Bowl XVIII later that season.
Haynes played only five games in 1983, and the Raiders’ Defensive Passer Rating actually increased from the previous season. However, when Haynes played the full 16 games in 1984, those numbers improved, but only slightly, even when Haynes played with fellow great Lester Hayes.
  • 1982 Raiders defense: 193 of 375 (51.5%), 2288 net yards, 7.0 YPA, 11 TD, 18 INT, 63.8 Defensive Passer Rating
  • 1983 Raiders defense: 282 of 531 (53.1%), 3162 net yards, 6.9 YPA, 20 TD, 20 INT, 71.8 Defensive Passer Rating
  • 1984 Raiders defense: 254 of 508 (50.0%), 2752 net yards, 6.4 YPA, 19 TD, 20 INT, 66.6 Defensive Passer Rating
Deion Sanders (Atlanta Falcons 1989-93, San Francisco 49ers 1994, Dallas Cowboys 95-99, Washington Redskins 2000, Baltimore Ravens 2004-05)
At first sight, the impact of Neon Deion joining two new teams at his prime couldn’t be better. When signing with the 49ers in 1994 and Cowboys in 1995, those teams won the Super Bowl later that year. The first true free agent star at the cornerback position, Sanders definitely created a win-win for his team in the mid-90s.
However, the rings don’t tell the whole story. Both the 1994 49ers and 1995 Cowboys already had championship-caliber teams, so signing Sanders only provided the cherry on top the sundae. Furthermore, while San Francisco’s Defensive Passer Rating improved from 16th in 1993 to 5th in 1994, the Cowboys saw no improvement in 1995, even when Deion’s nine games are accounted for alone.
  • 1993 49ers defense: 314 of 564 (55.7%), 3197 net yards, 6.2 YPA, 23 TD, 19 INT, 74.0 Defensive Passer Rating
  • 1994 49ers defense: 329 of 583 (56.4%), 3501 net yards, 6.4 YPA, 15 TD, 23 INT, 68.1 Defensive Passer Rating 
  • 1994 Cowboys defense: 269 of 522 (51.5%), 2752 net yards, 5.8 YPA, 19 TD, 22 INT, 64.0 Defensive Passer Rating 
  • 1995 Cowboys defense overall: 293 of 523 (56.0%), 3272 net yards, 6.7 YPA, 17 TD, 19 INT, 72.3 Defensive Passer Rating 
  • 1995 Cowboys defense with Sanders: 155 of 285 (54.4%), 1879 net yards, 6.9 YPA, 7 TD, 9 INT, 71.3 Defensive Passer Rating
Rod Woodson (Pittsburgh Steelers 1987-96, San Francisco 49ers 1997, Baltimore Ravens 1998-2001, Oakland Raiders 2002-03)
Before working as an NFL Network analyst, Woodson helped the 2000 Ravens make a dominant defensive run en route to a Super Bowl XXXV triumph. Baltomore surrendered just 10.3 PPG, the fewest of any team in the Live Ball Era, and were dominant in the playoffs, too. By all means, Woodson played a key role in building an all-time great defense. However, Baltimore didn’t see an immediate improvement on defense when Woodson signed with the Ravens in 1998. Perhaps it’s even more surprising to see these numbers when the Ravens started long-forgotten cornerbacks Antonio Langham, DeRon Jenkins, Donny Brady and Eugene Daniel in 1997.
  • 1997 Ravens defense: 332 of 556 (59.7%), 3673 net yards, 7.1 YPA, 20 TD, 17 INT, 80.8 Defensive Passer Rating 
  • 1998 Ravens defense: 316 of 539 (58.6%), 3592 net yards, 7.2 YPA, 20 TD, 17 INT, 80.1 Defensive Passer Rating 
Aeneas Williams (Phoenix/Arizona Cardinals 1991-2000, St. Louis Rams 2001-04)
Williams provides the one exception to this trend, but other factors also played into this dramatic change. The horrible 2000 Rams defense received a total defensive overhaul. Offseason additions included Williams, defensive coordinator Lovie Smith and three first-round draft picks. The improvements sparked St. Louis to a Super Bowl XXXVI appearance.
  • 2000 Rams defense: 323 of 534 (60.5%), 3797 net yards, 7.6 YPA, 32 TD, 19 INT, 89.5 Defensive Passer Rating 
  • 2001 Rams defense: 314 of 541 (58.0%), 3097 net yards, 6.2 YPA, 16 TD, 21 INT, 69.9 Defensive Passer Rating 
Champ Bailey (Washington Redskins 1999-2003, Denver Broncos 2004-present)
Before Asomugha stole his thunder, Champ Bailey garnered comparisons to the all-time great cornerbacks. At the top of his game, Bailey swapped team in a rare player-for-player trade.
During a time Denver almost regularly showed serious potential before fading late in the season, it was the perfect time for an elite cornerback like Bailey to make a major free agent impact and send the Broncos to Super Bowl contention. Instead, Denver’s defense put up nearly identical numbers, and the Broncos faded again late in the 2004 season.
  • 2003 Broncos defense: 265 of 495 (53.5%), 2828 net yards, 6.2 YPA, 17 TD, 9 INT, 76.2 Defensive Passer Rating 
  • 2004 Broncos defense: 272 of 484 (56.2%), 2947 net yards, 6.6 YPA, 17 TD, 12 INT, 78.0 Defensive Passer Rating
As this list shows, the fans’ chants for free agents should not end with Asomugha. While he may be one of the league’s best cornerbacks, he won’t change a defense’s fortunes by himself.