It always comes down to the baton pass. In 2008, the U.S. men and women were the heavy Olympic favorites in the 4x100 meter relay. Then both teams dropped batons, disqualifying themselves and becoming a worldwide cautionary tale: relays are made by good teams, not great individuals.
At the 2014 IAAF World Relays, the U.S. women were not favorites in the 4x100. That would go to Jamaica, led by two-time 100m gold-medalist Shelly-Ann Fraser-Pryce, who was assigned the anchor leg.
Despite her repeated assurances that she would run, Fraser-Pryce was an inexplicable no-show Saturday night on the track. It led to Jamaica's terrible handoff between the third and fourth legs—where Fraser-Pryce was supposed to be—allowing the U.S. to capitalize on a lead from a monster third leg by Jeneba Tarmoh. Where Jamaica balked, Tarmoh's pass to anchor LaKeisha Lawson was flawless, and she ran in uncontested for the win.
True, a few of both countries' best sprinters stayed home. But when the pressure was on, the U.S.'s teamwork came through while Jamaica was left hamstrung by their greatest athlete.
UPDATE: Well, the U.S. hasn't completely fixed itself; the men's 4x200 was disqualified after a bad pass between the second and third legs.