A key milestone would be the first occasion of tear gassing of peaceful protestors in decades, which at the time was directed by the chief executive C Y Leung, and this  sparked backlash from the public and precipitated the Umbrella Movement.
A crucial point would be the use of tear gas on non-violent protesters for the first time in years, which was directed by top official C Y Leung, leading to widespread discontent and sparking the Umbrella Movement.