This one, I think, is a little bit different than the Lemode-mgz advertising redirect, or "malvertising" problem.
From the research I've done, this variant (of many similar kinds) is likely some sort of malware, perhaps from an unscrupulous browser add-on or toolbar. Many times these are installed with your "consent" (a poorly written, not obvious checkbox you didn't notice) when you add something else you want.
Please note: DBR and SBNation have no capacity to download anything to your browser. But whatever triggers the popup could happen on DBR as well as any website.
What to do? Do a virus scan. Be sure you update the virus signature file (aka virus definitions) before scanning. If that comes up clean, you might try following
these instructions. Be sure to read carefully. Plan on about 20 minutes (and be happy when you finish quicker). If there's anything you don't understand on that page, call your favorite tech person. These instructions are fairly easy to follow and will require downloading a different anti-malware tool called adwcleaner. Why a second tool? There are SO many viruses/malware/crapware/scumware out there, sometimes your favorite tool hasn't quite gotten around to that particular issue. Sometimes another tool will pick it up.
If that still doesn't work (or if you don't want to do the above step), go to your browser's help file to figure out how to uninstall toolbars, plug-ins, add-ons, and extensions. These are things that are written by third-parties to enhance the browser's functionality -- or do something evil. Follow those instructions. If there's ANYTHING you don't recognize, uninstall it. If it was just recently installed, uninstall it. If you installed it and have used it regularly for years, it's likely not the problem. You're looking for weird stuff. (Don't know what toolbars, plug-ins/add-ons are? You're probably safe to get rid of them all! Unless you recognize them from national sites, like Adobe, Google, iTunes, etc.
Deleting cookies and history can help, as that may eliminate some triggers for the popup (and it may come back later).
Feel free to ask questions. We'll see if we can help. I'm not a virus/security expert, but I'm pretty competent at trying to remove them. (I'm most skilled with Windows and Firefox, but can help with other browsers and even sometimes Mac).
We are on the web, and as such, we are all vulnerable to malware. We all have to be careful online. But we also need to know that the bad guys will do their best to cover their tracks and make it look like the problem lies elsewhere. That's one reason why these things are so difficult to figure out.