He got caught in a time distortion and wound up on Earth in the early 21st Century. He was able to survive by becoming a construction contractor in Star's Hollow Connecticut.
Wow I've never had such fun reading an article. Completely surprised when I got to the director part that it was Wil Wheaton himself writing it. Thanks for linking it.
The Greatest Generation latched onto this early and started seeking out every trading card featuring and signed by Biff Yeager, such that they actually created a bubble and raised the value of Chief Argyle cards.
As a result, a "Natural Yeager" as they call it currently goes for almost $300 on eBay. By comparison, a similar signed Jonathan Frakes card goes for around $100.
He accidentally beamed down to a 21st Century American Public School. He noticed it was raining. Then he asked how much rain had fallen, and the teacher said about a third of an inch. Puzzled, he looked at her and said, 9mm? When the students heard the 9mm command, that's when the shooting started...