You've seen it several thousand times. After the ball is kicked, a group of three to four players, usually offensive linemen, stand shoulder to shoulder and wait for the call. The call comes from the return man, who hasn't fielded the ball. When he yells "Go!" the wedge starts upfield, providing a shield for the kick returner. As the kickoff-coverage team tries to locate the ball, small cracks, or seams, are formed. When the returner finds one of these seams, he bursts through it and hopes for the best.
1hMarc Stein and Marc J. Spears