The Slytherin Quidditch Team “flatten” Gryffindor in the final Quidditch match the previous year, according to McGonagall (PS9).
The new Gryffindors are reminded of the history during their first evening by Nearly Headless Nick
“Gryffindor have never gone so long without winning. Slytherin have got the cup six years in a row!” (PS7)
After a hard Quidditch practice, Harry thinks
“If they won their next match, against Hufflepuff, they would overtake Slytherin in the House Championship for the first time in seven years. ” (PS13).