How much does jet lag affect performance?

Dramatically.

By betting on west coast teams in every Monday Night Football game where they played east coast teams you’d beat the point spread 70% of the time.

NFL teams that crossed three time zones for a game “were twice as likely to be beaten by a lower-ranked opponent in the tournament’s first round.”

On the flip side, competing while their body is at the peak of its circadian rhythm increased performance of long jumpers by 4%. “…in sports as varied as running, weightlifting, and swimming, athletes competing when their bodies experienced the second boost of circadian energy were more likely to break a world record.”

Via Dreamland: Adventures in the Strange Science of Sleep:

The Stanford researchers dug through twenty-five years of Monday night NFL games and flagged every time a West Coast team played an East Coast team. Then, in an inspired move, they compared the final scores for each game with the point spread developed by bookmakers in Vegas. The results were stunning. The West Coast teams dominated their East Coast opponents no matter where they played. A West Coast team won 63 percent of the time, by an average of two touchdowns. The games were much closer when an East Coast team won, with an average margin of victory of only nine points. By picking the West Coast team every time, someone would have beaten the point spread 70 percent of the time. For gamblers in Las Vegas, the matchup was as good as found money.

And:

“The kiss of death is shifting three time zones,” he said. Teams that flew to the opposite coast were twice as likely to be beaten by a lower-ranked opponent in the tournament’s first round. Circadian schedules trumped natural ability. The circadian advantage— or disadvantage, depending on your perspective– popped up in studies of figure skaters, rowers, golfers, baseball players, swimmers, and divers. Everywhere you turned, there was evidence of the body’s hidden rhythms at work. One study found that in sports as varied as running, weightlifting, and swimming, athletes competing when their bodies experienced the second boost of circadian energy were more likely to break a world record. Long jumpers, for instance, launched themselves nearly 4 percent farther when the body was at its circadian peak. But the circadian rhythm cut both ways. Athletes competing when their circadian rhythm corresponded to the so-called sleep gates— those times in the early afternoon or late nights when it’s easy for most people to fall asleep— consistently performed a little worse than normal, even if the slowdown wasn’t obvious to them.