100m (Mario & Sonic at the London 2012 Olympic Games for 3DS)
From the Super Mario Wiki
100m is an Event that appears in the Athletics category of the Nintendo 3DS version of Mario & Sonic at the London 2012 Olympic Games. In this event, the characters race to get to the finish in the fastest time. The starting world record for this event is 9.58, and the starting Olympic record is 9.69.
100m appears as the first challenge of the Mario Episode 1 Stadium Blues, in which Mario must beat a Fog Imposter of Sonic. It also appears as part of the fifth challenge alongside Fencing - Epée and Judo and the sixth challenge with Pole Vault and Marathon in Heroes Episode 1, Mario and Sonic, in which Mario must beat a Sonic Fog Imposter in the fifth challenge and Sonic must beat Fog Imposters of Mario, Luigi and Tails in the sixth. It appears again as part of the first challenge in Heroes Episode 5 The Promise to Toad, in which Mario must beat Fog Imposters of Luigi, Sonic and Tails in it alongside Marathon and 100m Freestyle. It also appears as the fourth challenge of the Final Episode The Grand Showdown, in which Sonic must beat Dr. Eggman after he has been powered up by the Phantasmal Fog.
The event starts with the characters lining up on the starting line preparing to run. During this time, the player can hold to charge up their character. If they charge their character for long enough, they will perform a Start Dash. When the announcer says go, the player must release to start. The order in which the runners release the A Button determines their starting position at the end of the race. The camera then turns to depict the runners from the side, with the player who released A first leading, and the player must then quickly press to sprint to the finish. However, if they press the A Button too quickly too fast, their character will slow down again before they reach the finish, but will keep on running.
1) Start: Hold the A Button, and then release.