Freestyle
Technically, a swimmer can use any stroke in a freestyle event. In practice, everyone swims front crawl because it is fastest. Arms alternate in an overhead pull, kick is a flutter kick from the hips, and the head rotates to breathe rather than lifting. Flip turns at the wall. No rules about arm or leg position except during the individual medley relay legs.
Backstroke
Swimmers start in the water and push off the wall on their back. Arms alternate in a windmill pattern, kick is flutter kick on back. Backstroke flags hang five meters from the wall to warn swimmers that the turn is coming. Swimmers must touch the wall on their back during a turn, then flip. Finishing on anything other than the back is a disqualification.
Breaststroke
The most technical stroke and the one that generates the most disqualifications at the youth level. Arms must pull simultaneously and stay in front of the shoulders during the pull phase. Legs must kick simultaneously in a frog-kick pattern, and both feet must be at the same height. Any asymmetry in the kick is a DQ. Turns and finish require two-hand simultaneous touch. Breaststroke has the strictest rules of any stroke.
Butterfly
Both arms pull simultaneously over the water and recover together. Dolphin kick: both legs together in an undulating wave movement. No flutter kick is allowed. Turns and finish require simultaneous two-hand touch, same as breaststroke. Butterfly is physically the most demanding and is usually the last stroke young swimmers add.
Individual medley (IM)
Swimmers complete all four strokes in order: butterfly, backstroke, breaststroke, freestyle. Each stroke must be swum correctly or the entire event is a disqualification at the turn.
Why disqualifications happen at youth meets
Almost always breaststroke kick or IM transition violations. Judges are watching for one-arm touches, incorrect breaststroke kick, and backstroke swimmers rolling past horizontal before the touch.