If you can make an opponent stumble you can take him down: takedowns on an opponent in good stance are never easy. Takedowns on an opponent stumbling out of balance due to some preliminary attack are much easier by comparison. Creating a stumble can be done many ways but one of the best is the use of your feet – ashi waza – just as stepping into a curb mid step will trip and stumble you in everyday life, so too a well placed/timed foot will cause you to stumble. If you can then time a takedown in the midst of a stumble what previously seemed very difficult can now become surprisingly easy
