"Harry felt two large thumps as Fred and George hit them; then Angelina, Alicia and Katie’s voices, "We've won the Cup! We've won the Cup!" Tangled together in a many-armed hug, the Gryffindor team sank, yelling hoarsely, back to earth." (PA15)
In this match, the Slytherin team members resort to dirty tactics to try and beat Gryffindor’s team in the last Quidditch match of the year. However, in spite of Slytherin’s efforts to foul and cheat, Harry Potter catches the Snitch and Gryffindor wins the Quidditch Cup. The final score is Gryffindor 230 – 20 Slytherin (PA15).
Although the last Quidditch match of the season at Hogwarts usually takes place in early May; this one is taking place "on the first Saturday after the Easter holidays" (PA15), so should have been to mid-April by the real-world calendar. However, June weather and exams follow quickly afterwards (PA16), so May makes more sense.