In the vast majority of cases scissor kicks are caused by crossovers:
The swimmer crosses over the centre line in front of the head, over-rotates and then the legs scissor apart to stop them flipping over onto their back. Over time this becomes a habit in the stroke and feels normal - in fact most swimmers with a scissor kick don't even realise it is there.
In a sense the swimmer doesn’t have two problems but one. Remove the crossover and the scissor kick disappears permanently all by itself. But try to tackle the scissor kick directly with kicking drills and it keeps coming back without first removing the crossover.
How to remove the crossover? By improving your posture and alignment in the water using side kicking exercises, thinking about drawing your shoulders together and back to bring the lead arm straight:
Read the full description of this drill here.
Swim Smooth's Cause And Effect Methodology
Crossovers-causing-scissor-kicks is the most famous example of our "Cause and Effect" approach to stroke correction which is the backbone of all our coaching products. It's a philosophy which greatly simplifies stroke correction and hugely improves the chances of its success.
There are around 20 other C+Es that we employ at different times for different faults ranging from shortness of breath right through to mastering catch technique. Our best selling Book, DVDs and Swim Type correction guides all use this simple but powerful principle to permanently improve your swimming.