The 4 × 100 metres relay or sprint relay is an athletics track event run in lanes over one lap of the track with four runners completing 100 metres 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, marking the earliest point at which the outgoing runner may begin (giving up to 10 m of acceleration before entering the passing zone).

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.

The Honourable Usain St. Leo Bolt, OJ, C.D. ( /ˈjuːseɪn/; born 21 August 1986), is a Jamaican sprinter and a five-time World and three-time Olympic gold medalist. He is the world record and Olympic record holder in the 100 metres, the 200 metres and (along with his teammates) the 4×100 metres relay. He is the reigning Olympic champion in these three events, and is one of only seven athletes (along with Valerie Adams, Veronica Campbell-Brown, Jacques Freitag, Yelena Isinbayeva, Jana Pittman, Dani Samuels) to win world championships at the youth, junior, and senior level of an athletic event.

Bolt won a 200 m gold medal at the 2002 World Junior Championships, making him the competition's youngest-ever gold medalist at the time (since surpassed by Jacko Gill). In 2004, at the CARIFTA Games, he became the first junior sprinter to run the 200 m in less than 20 seconds with a time of 19.93 s, breaking the previous world junior record held by Roy Martin by two-tenths of a second. He turned professional in 2004, and although he competed at the 2004 Summer Olympics, he missed most of the next two seasons due to injuries. In 2007, he broke Don Quarrie's 200 m Jamaican record with a run of 19.75 s.

Michael Fred Phelps (born June 30, 1985) is an American swimmer who has, overall, won 16 Olympic medals—six gold and two bronze at Athens in 2004, and eight gold at Beijing in 2008, becoming the most successful athlete at both of these Olympic Games editions. In doing so he has twice equaled the record eight medals of any type at a single Olympics achieved by Soviet gymnast Alexander Dityatin at the 1980 Moscow Summer Games. His five gold medals in individual events tied the single Games record set by compatriot Eric Heiden in the 1980 Winter Olympics and equaled by Vitaly Scherbo at the 1992 Summer Games. Phelps holds the record for the most gold medals won in a single Olympics; his eight at the 2008 Beijing Games surpassed American swimmer Mark Spitz's seven-gold performance at Munich in 1972. Phelps' Olympic medal total is second only to the 18 Soviet gymnast Larisa Latynina won over three Olympics, including nine gold. Phelps also holds the all-time record for most gold Olympic medals, at 14.