Complex sentence: Standing up to him for the first time, George knocks Biff out and a smitten Lorraine follows George to the dance floor where they kiss for the first time ensuring Marty's existence.
Split into simpler sentences: Standing up to him for the first time, George knocks Biff out. A smitten Lorraine follows George to the dance floor, where they kiss for the first time, ensuring Marty's existence.