CPI(M) and Left Front activists carried placards condemning the 'assault' on Yechury.
Two persons were held in connection with the incident, which took place just before Yechury was about to address the press on the conclusion of the party's two-day politburo meeting here.
Hinting at RSS hand in the incident, the party said it would not be cowed down by the "Sangh's 'goondagardi' (hooliganism)" aimed at silencing its voice.