In Olympic swimming, there are four different strokes: butterfly, backstroke, breastbroke, and freestyle. Many of the rules in swimming tend to differ by stroke and event, but there are some general rules that apply to every event.
Each race must begin with what is called a start. A dive is used for all freestyle, breaststroke, butterfly, and individual medley events, while backstroke and medley relay events begin in the water. For starts on the block, swimmers will step on to the blocks after one long whistle from the referee. On the command "take your mark," swimmers will get into a crouched position, one foot in front of the other. Once each swimmer is set, there will be a signal to start the race, in which swimmers dive in and begin the competition. For backstroke, the swimmers will jump into the water and grab the handles on the front of the starting block. The swimmers will get into their start position on the command "take your mark," pushing off of the wall to begin the race at the sound of the starting signal. If a swimmer enters the water before the starting signal sounds, they are immediately disqualified from the race.
Swimmers in individual must complete the entire distance of the race, with relay distances evenly divided between the four members of the relay team. The swimmer must stay in the same lane for the entire duration and all turns must be made using physical contact off of the wall and swimmers cannot touch or push-off the bottom of the pool. In terms of the actual pool itself, it must be 50 meters in length with eight 2.5 meter wide lanes.
At least some part of the swimmer's body must touch the wall at each turn and the end of the race. The swimmer's head has to break the surface of the water at most 15 meters into the race.
In the backstroke start, swimmers cannot curl their toes over the gutter of the pool or the top of the touchpad. They must swim the entirety of the race on their back, except for the one stroke allowed within the flags to execute a flipturn. The swimmer must emerge from the water by 15 meters and must finish the race by touching the wall on their back.
Swimmers are allowed one butterfly kick under the surface of the water between a start or turn and breaking the surface of the water. The swimmer cannot turn on their back at any point during the race. The feet have to be turned outward on the kick and upon breaking the surface no downward kicks are permitted. The swimmer is required to contact the wall with two hands at each turn and the end of the race.
Swimmers are not allowed to swim on their back at any point during the race. Both arms must be moved forward simultaneously and both legs must be kicked together in a downward motion. All swimmers must touch the wall at each turn and the conclusion of the race with both hands.