To connect the knee with an agressors leg at high velocity.
The gern is effective due to its ability to incapacitate the target leg. Therefore preventing any chance of the target retaliating with a chase.
To increase the effectiveness of the gern, it can be combined with a leap. There is a positive correlation between length of run-up and the gerns effectiveness.
When using the gern, accuracy is paramount. A miss can lead to a swift retaliation, usually a John
in the head.
Proper gern technique is hard to master.