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I know this isn't breaking news or anything, but the internet is a terrific resource. In the five or so years I've been online, I've gotten information about all sorts of things that interest me: baseball, basketball, football, blackjack, card tricks, running, PERL, anagrams, Tulsa restaurants, planimeters, and groupoids just to name a few. Most of what I've learned hasn't come from commercial sites, but from individuals simply sharing what they know. I've taken so much from these people that I can't possibly repay them. What I can do, however, is contribute to the community and create a site that, hopefully, other people can get something out of.
And that is exactly what you can do. If you find pro-football-reference.com useful, and you want to repay me for the work I put into it, repay me by contributing your own time, information, or knowledge to create a site that other people can benefit from.