Hall is a devout, pencil-thin 28-year-old who's already covered 26.2 miles faster than any American ever -- a 2:04:58 time at the Boston Marathon in April that didn't count as a U.S. record because the course does not meet specifications.

On top of that, he came in fourth, trailing two Kenyans and an Ethiopian.

In Sunday's Chicago Marathon, Hall figures to again have his hands full with the five Kenyans -- including favorite Moses Mosop -- two Ethiopians, a Brazilian and Japanese ranked alongside him in the top 10.

"The marathon is like boxing, anything is possible on any given day," Hall said Tuesday. "Sometimes a guy who hasn't built a resume yet hits that magical day where everything clicks."

An American hasn't had a day like that at the Olympics since Frank Shorter won gold in 1972, then came back four years later for a silver. The only medal won by an American since came in 2004 when Meb Keflezeghi took silver in Athens.

And Keflezeghi -- who moved to the United States at age 12 and began racing in junior high, but didn't become a naturalized citizen until graduating from UCLA in 1998 -- was able to win silver only after leader Vanderlei de Lima was ambushed by a protester late in the race.

Hall finished 10th at the Beijing Olympics. On the heels of his performance in Boston, a win in Chicago would give him momentum going into next January's U.S. Olympic trials. It would also be the first win in a major race by an American since Keflezeghi claimed the 2009 New York City Marathon.

"Somebody could write a dissertation about all the things we've been doing wrong," said Greg Meyer, who was the last American to win the Boston Marathon -- in 1983 -- and will work the radio broadcast for the Chicago race.

"Running in college now is mostly about time trials, and if you do reach world-class levels, the economics of the sport are such that the top guys don't need to race much. Maybe it's sour grapes from an old man, but with our shoe contracts, maybe half the money was bonuses based on appearances. We had to run to make a living. ...

"Compare that with the Kenyans. Growing up, we ride school buses, they run to school. A lot of promising guys here get college degrees, give running a shot, right, and if it doesn't produce results right away, they look for something else to make a living. In Kenya, if you show promise, running is your best, maybe only shot to make a living.

"There's a certain amount of learning that only comes with racing ... but it's like we've looked around at all the great African runners and just conceded, "This is who we are. We're not going to win on this stage.'"

Hall doesn't buy into that last bit, though in order to climb up the sport's ladder, he's had to learn to run like the Africans.

Hall's strength, since he began running seriously at age 14, has been eating up miles at a steady clip like a metronome. His toughest competitors, on the other hand, surge several times over the course of a marathon, breaking away in small packs for the lead, then surging again to test one another as the finish line approaches.

"I'm realizing more and more how important it is for me to maintain contact. That's something I did well at Boston this year, where guys would get away from me," he said in an interview this summer with a Stanford alumni magazine.

"That's how I stay in the front, but how do I win the race? That's a whole different question," he added. "That's what I'm starting to address now."

It hasn't been a smooth progression.

Hall began running in eighth grade, when his size -- 5-feet and barely 100 pounds -- narrowed his choice of sports, but he loved competitive racing from the very start. He's 5-10 and 140 pounds now, but still loves to run, maybe too much.

After years of training maniacally and often racing both spring and fall marathons, he's finally begun taking adequate time off to rest and let his body heal. Hall learned the dangers of overworking a year ago, when nagging injuries forced him to pull out of the Chicago race, leaving him with another score to settle.

"Dropping out turned out to be good. I learned a lot about myself, and what my body can take. Now that I have my health squared away, the sky is the limit. I believe my best days are not only in front of me," he said, "but maybe in front of for a long time."

We may find out if he's right as early as Sunday.

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Jim Litke is a national sports columnist for The Associated Press. Write to him at jlitke(at)ap.org. Follow him at http://twitter.com/JimLitke.