Major Inner Reaping
Use this technique often when your opponent is standing in a self-defense position open to the side with their legs spread wide. It is even more effective if they are leaning backward at the waist. You actually clip your opponent’s foot with the foot you are not using as a support. They will fall over backwards. Here is a photo of o uchi gari used in the 2003 World Masters.
Ashiwaza II by World Champion Michael Swain is an excellent examination of several leg techniques (Ouchi gari, Kouchi gari, Kosoto gari and Hiza guruma) including many effective variations and follow-ups. Part of the Ippon Books Masterclass Series, it shows excellent competition versions of Ouchi gari.
Here is a Lesson on Ouchi Gari, a video of Ouchi Gari, and another video of Ouchi gari.