"They were an unruly group of people who started in the afternoon by blocking off the roads," said Brigadier Hangwani Mulaudzi.
About 300 supporters of expelled ANC Youth League president Julius Malema converged outside the Holy Worship Church hall, in Thohoyandou, before Zuma arrived.
They carried banners with Malema's picture and sang: "Zuma is troubling us".
They became involved in a fight with ANC security officers when the entered the hall at 4pm.
"Those people are anti-Zuma and came inside the venue and started singing anti-Zuma songs. Then the ANC security inside the hall contained them and assaulted them," said Mulaudzi, adding that the police were called in to defuse the situation.
"Five of them, who were among those singing anti-Zuma songs, were bundled into a police van and taken away from the venue.
"We then gave them a serious warning to refrain from causing problems in the area. They complied and were released on a warning."
Pelted with rocks
Mulaudzi was unable to say what happened to the security officials who assaulted them.
Zuma began speaking after 5pm. Violence continued outside the hall during his address.
"They continued to cause a disruption. Even when president Zuma started and was busy with the lecture, they were pelting police with stones," said Mulaudzi.
"We had to use a water cannon to disperse them … We have now neutralised them. The situation is under control."
Zuma's lecture was about the legacy of former president Nelson Mandela.
Part of it touched on the history of the youth league in Mandela's time.
Mandela and his friend Oliver Tambo were founding members of the ANC Youth League, which was established in 1944.
"The ANC youth was impatient with the leadership of the time, whom they felt were too gentlemanly in their approach to the struggle," said Zuma.
A magnet through persuasion
He likened Mandela to a "magnet" which attracted people "through persuasion".
"Inside our country, even those who were, and who are still, fundamentally opposed to the ANC, and who fought tooth and nail to keep South Africa a racist pariah state, now claim Nelson Mandela as their own," said Zuma.
"Such is the power of Nelson Rolihlahla Mandela, a unique and great statesman who is able to win over even his enemies."
During the first 10 years of democracy, five of which were under Mandela's leadership, 789 laws or amendments aimed at removing apartheid laws, were approved by Parliament.
"He [Mandela] worked tirelessly to change South Africa for the better," said Zuma.
Madiba remained a loyal and disciplined member of the ANC through "thick and thin", he said.
"The abiding lesson to us is that all South Africans should continue the reconciliation project that he so passionately led on behalf of the ANC.
"Our differences should not set us apart from one another, but should be the compelling reason for us to draw closer to forge a common future, all of us, black and white."
Hills to climb
Zuma said South Africa still had many hills to climb.
One of them was social and economic emancipation, as outlined at the party's policy conference last week.
"One hill that we must climb together is one taking us to true economic and social emancipation," said Zuma.
"As the ANC we have outlined the vision of economic emancipation … We look forward to tangible resolutions at the national conference in Mangaung on the economy, taking forward our discussions at the policy conference last month."
On Wednesday, the ANC will be in Mvezo in the Eastern Cape, Mandela's birthplace, to launch the Nelson Mandela Legacy Bridge over the Mbashe river.
Zuma's spokesperson Mac Maharaj could not immediately be reached for comment on the violence. – Sapa