This all started with a tweet. Well, by this I mean this post. Charles Tillman started long before Twitter did, but I’m getting way off the subject here, which is a great way to start a post isn’t it?

Anyway, free agency starts on Tuesday, and there’s a good chance that Charles Tillman will be signing with a team that isn’t the Chicago Bears. He’d be the latest departure in what has been an exodus of the stars of the last Bears team to reach the Super Bowl, as the team tries to get younger.

Last year Bears fans said goodbye to Brian Urlacher, just this week we got confirmation that Devin Hester won’t be back, and Tillman will probably follow. It would just go against the trend that we’ve seen with this Bears front office to get younger by bringing back a 33-year old cornerback, even if he was the greatest cornerback in franchise history.

And now we’ve reached the point.

The tweet I alluded to came from Bears beat reporter Adam Jahns. Jahns said he received an email from a reader ripping him for writing that Tillman was “arguable the best cornerback in Bears history” in a recent story about Tillman’s impending free agency. Me being me, I asked Jahns if the email came from DWoolford@aol.com, and then a little conversation about Tillman began.

It was at that point I said to myself “well this would work as a nice Saturday afternoon post, wouldn’t it?” Whether it will or not, I’ll let you decide, but I’m writing the son of a bitch anyway.

Now, in my opinion, I don’t think there’s much question to the fact that Tillman is the greatest corner the Bears have ever had. In my mind he is, but sometimes it’s better to have facts to go with those opinions, so I did a little digging.

I could compare stats from great Bears corners, but instead I just took a look at Pro Football Reference’s “approximate value” stat. AV is a stat the site uses to do just what it sounds like: give the approximate value of a player to his team. Think of it as a kind of football WAR, though, as PFR itself says, don’t consider it the “end all, be all” of football stats.

Sadly, the stat only goes back to 1950, so players who played before then aren’t included.

That caveat aside — no offense to those players, but I’m pretty sure the players of today are much better than they were — using the AV stat drives home the point that Tillman was the greatest corner in franchise history, and really, it’s not even remotely close. While there are plenty of great Bears safeties in the past that compared to Tillman as far as AV is concerned, or even surpassed him — hey there, Gary Fencik — the gap between Tillman and other Bears cornerbacks is large. Part of this is due to the fact Tillman spent 11 seasons with the Bears, but longevity should play a role in this debate.

Here’s a list of the top 10 Bears cornerbacks of all time using AV.

*Shaun Gayle played both corner and safety during his time, but I included his career total

So, as I said, Tillman is the best and it wasn’t even close. What’s more remarkable about Tillman’s career in Chicago is that, while he’s always been good, he had his best seasons after turning 30. In his first eight seasons with the Bears, from age 22 to 29, Tillman had an average AV of 6.75 a season, peaking with a nine in 2006, and bottoming out with a three in 2004.

Then he turned 30 and in 2010 he put up an AV of 11. Which was pretty remarkable until 2011 came along and he had an AV of 16 at the age of 31. Now, unfortunately PFR doesn’t keep a database of the best single-season AVs in franchise history, but to give you an idea of how good an AV of 16 is, Walter Payton, Mike Singletary, Brian Urlacher and Dan Hampton — the four highest-ranking Bears in terms of career AV — had 13 seasons with an AV of at least 16 between them. Only Hampton and Payton had seasons of 16 or higher from the age of 31 or higher (Payton had two).

In other words, Charles Tillman’s 2011 season was an all-timer in franchise history, and he’s not just the best corner the team’s ever seen, but one of it’s best players period. Now, he doesn’t crack the top ten of all time (that chart is right below), but he did check in at No. 13.

Tillman, Gary Fencik, Richie Petitbon and Rosey Taylor are the only four Bears defensive backs to appear in the top 20, with Fencik the only DB in the top ten.

So if you want to make the argument that Tillman wasn’t the best defensive back the Bears have ever had, you’ve certainly got a case to make. But when it comes to the best cornerback?

Well, you just saw the numbers. You tell me.

Also, just in case you were wondering, the highest ranking quarterback the Bears have had using AV is a tie between Jay Cutler and Jim McMahon. Both are tied at No. 49 with 49.

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