Leg Sweeps and Take Downs

As Wikipedia states: "Karate's nage waza (投げ技 or throwing techniques) is the set of techniques whereby the opponent is thrown to the ground. While typical students of karate focus most of their attention on learning striking techniques, karate throws are considered indispensable for self-defense and, although not always taught, are part of the classical art.” 

The leg sweep or ashi barai (足掃) is similarly employed, and can be found in many kata. Including Gekisai Ichi, Gekisai Ni and Saifa. This video shows a karate style that emphasizes throws, sweeps and take downs, and such real applications should be borne in mind when practicing and performing kata