As per the wikipedia ‘The Fosbury Flop is a style used in the athletics event of high jump. It was popularized and perfected by American athlete Dick Fosbury, whose gold medal in the 1968 Summer Olympics (Mexico) brought it to the world’s attention. Over the next few years, the flop became the dominant style of the event and remains so today. Before Fosbury, most elite jumpers used the straddle technique, Western Roll, Eastern cut-off or scissors jump to clear the bar.
Given that landing surfaces had previously been sandpits or low piles of matting, high jumpers of earlier years had to land on their feet or at least land carefully to prevent injury. With the advent of deep foam matting high jumpers were able to be more adventurous in their landing styles and hence experiment with styles of jumping.