Judo and Karate Ashi barai timing

The foot sweep (called ashi barai in Karate and Judo) can be extremely effective. It can be used to distract your opponent while attacking in combination and sometimes can be used to take down opponents. There is one other way that it can be used to not only 99.99% of the time take down your opponent but also make him/her think twice about moving in to you, and if they cant move in to you, they cant hurt you. Your opponent will move in by moving his feet towards you, sliding, stepping or any other way. As they move in, there front foot will momentarily be off the ground and for that moment there balance is unstable. If you can sweep that front foot just before it lands back on the floor, whilst also being cautious of any oncoming attack, there is a high chance they will fall, and if they don't fall they will certainly lose there balance for you to carry on attacking. Psychologically it will also make them think twice about closing the gap. It requires a lot of practice and drilling but is very effective, and can be used by any martial artist.