Ashi tori (leg grab) when grip falters or you miss the chance to catch the leg midair. When you miss a chance there is still a timing of opportunity that most people miss!
Make sure you offset the weighted leg this has two functions.
1) it avoids an oncoming attack
2) it brings the weight off the front foot so it lands in your hand with little struggle
3) use your heel to feed their leg to you instead of your toes; anatomically this is more connected and stronger.