The 4 × 100 metres relay or sprint relay is an athleticstrack event run in lanes over one lap of the track with four runners completing 100 meters each. The first runners begin in the same stagger as for the individual 400 m race. A relay baton is carried by each runner and must be passed within a 20 m changeover box (usually marked by yellow lines) which extends 10 m on either side of each 100 m mark of the race. Another line is marked 10 m further back, which the outgoing runner must begin in front of to begin accelerating.
Transferring of the baton in this race is typically blind. The outgoing runner reaches a straight arm backwards when they enter the changeover box, or when the incoming runner makes a verbal signal. The outgoing runner does not look backwards, and it is the responsibility of the incoming runner to thrust the baton into the outstretched hand, and not let go until the outgoing runner takes hold of it. Runners on the first and third legs typically run on the inside of the lane with the baton in their right hand, while runners on the second and fourth legs take the baton in their left. Polished handovers can compensate for a lack of basic speed to some extent, and disqualification for dropping the baton or failing to transfer it within the box is common, even at the highest level.