A defensive player is illegally positioned (Section 18.1), and there is contact with the thrower; or
A defensive player is illegally positioned (Section 18.1), and there is non-minor contact between the illegally positioned defensive player and the thrower; or
If a defender is legally marking the thrower and then a second defender commits a double team, the second defender is deemed to be the illegally positioned defensive player. Therefore it would only be non-minor contact between the thrower and the second defender that would automatically result in a defensive throwing foul.