Which of the following is NOT a valid stroke in a swimming competition?

Leg stroke 

The correct answer is Option (3) → Leg stroke

- In competitive swimming, there are specific rules and regulations governing the allowed swimming strokes. The four main competitive swimming strokes recognized by FINA (the International Swimming Federation) are:

1. Freestyle: Swimmers use any stroke they prefer, typically the front crawl or the butterfly.

2. Backstroke: Swimmers swim on their back, and the arms move alternately over the head.

3. Breaststroke: Swimmers move both arms simultaneously in a circular motion and kick both legs in a frog-like motion.

4. Butterfly: Swimmers move both arms simultaneously over the water in a butterfly-like motion and perform a dolphin kick.

- "Leg stroke" is not a recognized swimming stroke in competitive swimming.