And this is why a decree from the 'High Inquisitor of Hogwarts'-Umbridge's made-up position to ensure her power and success at Hogwarts- came onto the notice boards in the common room. This decree announced that all clubs and teams were to be dissolved and needed permission to reform. 

This didn't just prevent the DA from rising. There was an added bonus for Umbridge- she exacted revenge on Potter for his latest 'misdeed' by including Quidditch teams in this decree. She immediately gave the Slytherin team permission- but refused the Gryffindor team. Minerva McGonagall had to directly appeal to Dumbledore to counteract her. 

Incomplete