Former Cosatu general secretary Zwelinzima Vavi and EFF leader Julius Malema are plotting to overthr.
A small but vocally powerful section of the audience, some clad in ANCYL colours, burst into a confrontational song as Zuma entered the hall: "Jacob Zuma Uphi u Juju, as'phelelanga" (Where is Julius Malema? We are incomplete without him).
The song was accompanied by hand gestures similar to those used by soccer supporters when they want a player replaced.
Malema, who is facing a five-year suspension from the ANC, has been leading youth league efforts to replace Zuma at the party's elective conference in Mangaung in December.
They also want secretary-general Gwede Mantashe to be replaced by Sports Minister Fikile Mbalula.
All hell broke loose halfway Zuma's speech when local youth league leader Loyiso Nkohla tried to plead with his comrades to stop interrupting the ANC president's lecture.
An SABC cameraman - Rudi le Roux - lay bleeding after being hit by a flying chair during the fracas.
He was rushed to the local Christian Barnard Memorial Hospital.
Police and Zuma's security personnel entered the fray and police frogmarched one of the rowdy Malema supporters out of the hall.
Zuma tried to ignore the fracas and carried on with his lecture.
Minister in the Presidency Trevor Manuel and his defence counterpart Lindiwe Sisulu tried to diffuse the stand-off between the police and the rowdy crowd to no avail.
Western Cape ANC provincial secretary Songezo Mjongile, ANC spokesman Jackson Mthembu and Keith Khoza also pleaded for calm, but their pleas fell on deaf ears.
At the end of his address, a red-faced Zuma apologised to members of the Makgatho family who were inside the hall for the lecture.
Addressing the unruly youths, Zuma said their conduct had revealed their true colours.
An angry Mthembu said: "We have got footage ... and cameras don't lie. If they are members of the ANC, working together with the provincial leadership we will be able to deal decisively with these scoundrels. "
Mthembu said it was "regrettable" that an SABC newsman had been injured during the commotion.