Whether by overbalancing your opponent, sweeping their legs from under them or some other means, you are able to get them into a prone position on the ground.
Before your melee attack declare you are attempting a Knockdown. Roll to attack as normal. If successful calculate damage as normal. If you beat the TN by 30 or more points your opponent falls to the ground prone until the end of the next round. While prone they may not move faster than a crawl, which is ¼ of their Physical Agility in metres rounded up to the nearest metre.
Each additional time you purchase this Ability your chances of a successful Knockdown improve by 10 points.