Wikipedia
A counter-protest is a protest action which takes place within the proximity of another protest to which the counter-protest is in ideological opposition. The purposes of counter-protests can range from merely voicing opposition to the objective of the other protest to actively drawing attention from nearby media outlets away from the other protest toward the counter-protestors' cause to actively seeking to disrupt the other protest by conflict of a non-violent or violent nature.
In many countries where protests by various pressure groups are allowed, the nearby law enforcement installation may make it a priority to keep rival protestors as far from each other as to avoid possible physical contact, and legal contention often arises over whether the rival groups possess permits to gather and rally within short distance of each other. Often, rallies can be infiltrated by rival protestors for purposes ranging from distraction, disruption to merely asking critical questions of the leaders of the rally or providing humorous or mocking diversions; the reactions of protestors to counter-protestors within close proximity can often be violent and confrontational.
In some countries, governments can even sponsor counter-protesters who rally against opposition figures and members.