Matthew Stephen Leinart (born May 11, 1983 in Santa Ana, California) is an American football quarterback for the Arizona Cardinals of the National Football League. He played college football at Southern California, leading them to an AP national championship in 2003, a BCS national championship in 2004, and an appearance in the BCS National Championship game in 2005. Leinart earlier played quarterback at Mater Dei High School. In 2004, his junior year at USC, he won the Heisman Trophy. He also won the inaugural Manning Award for college quarterbacks in the same season.

Leinart was born in Santa Ana, California. He was born with strabismus (“crossed eyed”), as his left eye was not aligned correctly with his right. He underwent surgery when he was three years old and was fitted with special glasses to correct the problem, but the eyewear combined with Leinart's already-overweight frame to make him an easy target for ridicule at the hands of other children. “I used to get made fun of for being cross-eyed. It's just a terrible thing because kids are so cruel to the fat kid, to the kid with the glasses. So I turned to sports,” he would later say.

Leinart attended Mater Dei High School and was a student and a letterman in football. As a junior, he led his team to a California Interscholastic Federation Division I co-championship, and was named the Sierra League's Offensive Most Valuable Player. Wearing the same number 7 he does today with the Cardinals, he was chosen as the Gatorade California high school football player of the year.