What happens next?

How to prevent breaststroke swimmer's knee 
Recognize your kind of kick, and pay attention to your technique. 
Based on the kind of competitive distance you are specialized, the width between the knees when doing the kick varies. Usually, sprinters tend to do their kick with their knees closer than mid-distance or imers.

Possible answers:
(1). If you do not want to hurt yourself, you do not need to fall backwards, or stop suddenly. You should also be alert to your position..
(2). Pedal with your left foot, not your right. Use your outside arm to pull the leg forward..
(3). This makes the angle of the knees with the ankles be more sharp, which at the end makes sprinters more likely for knee injuries. The most important thing is to make sure every kick is not out of the boundaries of the knee rotation, especially during the out sweep of the kick..
(4). Kicking from the hip, not from the chest is much harder, especially towards the base of the kick. As you grow older, the angle between the knees will shift from right to left..
(3).