Prosecutors told jurors Thursday that a Texas teenager competing at a high school track meet provoked a 17-year-old athlete from a rival team before fatally stabbing him in the stadium's bleachers as other students looked on.

An attorney for Karmelo Anthony said his client did not instigate the fight with Austin Metcalf, telling the jury at the start of a packed murder trial near Dallas that it was instead an act of self-defense.

Anthony pleaded not guilty to last year's stabbing, which stunned an affluent suburb where the pair attended school.