“Total Football” is the label given to an influential tactical theory of association football in which any outfield player can take over the role of any other player in a team (save the goalkeeper). It was pioneered by Dutch football club Ajax from 1969 to 1973, and further used by the Netherlands National Football Team in the 1974 FIFA World Cup. It was invented by Rinus Michels, a famous Dutch football trainer/coach (who was the coach of both Ajax and the Netherlands national team at the time).
In Total Football, a player who moves out of his position is replaced by another from his team, thus retaining the team’s intended organizational structure. In this fluid system, no player is fixed in his nominal role; anyone can be successively an attacker, a midfielder and a defender. The only player fixed in his nominal position is the goalkeeper.
Total Football’s tactical success depends largely on the adaptability of each footballer within the team, in particular his ability to quickly switch positions depending on the on-field situation. The theory requires players to be comfortable in multiple positions; hence, it places high technical and physical demands on them.
— Wikipedia on Total Football