Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Mario Alejandro Ruíz Díaz (born January 12, 1977 in Morelia, Michoacan) is a Mexican footballer and defender. He currently plays for Club Leon. He started his career in 1997 with Morelia, where he became a symbol. In 2003 he was transferred to Tigres. Within the sport of association football, a defender is an outfield player whose primary role is to prevent the opposition from attacking. There are four types of defender: centre back, sweeper, full back, and wing back. The centre back and the full back positions are essential in most modern formations. The sweeper and wing back roles are more specialized for certain formations.