Perhaps you're thinking about:
* The Triwizard Tournament: This is a magical competition in the fourth book, *Harry Potter and the Goblet of Fire*. Harry Potter is the third champion, and he wins the tournament despite the challenges he faces. However, the prize for the tournament is not explicitly stated.
* The House Cup: This is a competition between the four Hogwarts houses (Gryffindor, Slytherin, Ravenclaw, and Hufflepuff) for the House Cup, awarded based on points earned throughout the year. Harry Potter is a Gryffindor, and his house wins the Cup in many books.
Could you please clarify your question? What do you mean by "third Harry Potter"?