In team sports like rugby and American football, defensive players positioned at the back of the field; also in soccer, defensive players on the sides.
From 'full' (complete, entire) plus 'back' (rear position), combining to describe players whose role spans the entire back defensive line.
The fullback position has evolved dramatically—in modern soccer, fullbacks are often the most athletic players, running the entire sideline both defensively and offensively, making them key to modern tactical systems.
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