A steal occurs when a defensive player legally takes possession of the ball from an opposing player during gameplay. A turnover is counted when a player with possession of the ball loses possession as the result of a violation or an opposing player.
In other words, a steal is made when a defender's aggressive action causes a turnover by either taking the ball away from the offensive player, intercepting a pass, or deflecting the ball away. Key: The steal is always credited to the defender who initially disrupted the ball.
So, who's fault is the steal/turnover? Did the defender take the initiative to take the ball? In that case, it is a steal. If the person dribbling makes a mistake (i.e passes and intercepted, travels, etc.) and that's how the opposing team gets the ball, then it's a turnover.