Key paragraph(s) can be found below the document.
39. While it is the duty of Contracting States to take reasonable and appropriate measures to enable lawful demonstrations to proceed peacefully, they cannot guarantee this absolutely and they have a wide discretion in the choice of the means to be used (…). In this area the obligation they enter into under Article 11 of the Convention is an obligation as to measures to be taken and not as to results to be achieved […].
40. However, the mere existence of a risk is insufficient for banning the event: in making their assessment the authorities must produce concrete estimates of the potential scale of disturbance in order to evaluate the resources necessary for neutralising the threat of violent clashes […].