Fullbacks are a position in American football and soccer that play a crucial role in both defense and offense. In American football, fullbacks typically line up behind the quarterback and are responsible for blocking for running backs, as well as carrying the ball themselves on short-yardage plays. They are often larger and stronger than other players, allowing them to effectively protect the ball carrier. In soccer, fullbacks are defenders positioned on the left and right flanks of the field. Their primary duties include preventing opposing players from advancing and supporting their own team's attacks by overlapping with wingers. Fullbacks must possess good stamina and tactical awareness to balance their defensive responsibilities with offensive contributions.