They said there was "a lot of precedent" for such a defence.
Rei-Marata Goddard, who is charged under the name Grace Goddard, said he planned to present evidence to prove police acted in an "incredibly violent and excessive manner".
Watson and Goddard are members of People Against Prisons Aotearoa.
Watson said the group attended training sessions before the protest to learn how to avoid accusations of violence. It included instructions to "turn your palms in so they can't accuse you of pushing them".
They said they were thrown on their heads and left bruised by police treatment, "but I don't have a concussion, thank God".
Goddard said he was dragged by his necklace and choked during the protest, as well as denied access to his "mobility aid", a walking stick, which he says was collapsed in half and thrown over a fence out of his reach.
"I believe I was treated in a way that severely undermined my human rights," he said.
Goddard and Watson appeared in court first this morning along with Gary Thomas Chiles. All three pleaded not guilty to the obstruction charges.
Supporters packed into the public gallery cheered and applauded the trio as they left the courtroom.
Tui Helen Kupa and Grant Sanders appeared later, without entering pleas. They were remanded to October 27, when Kupa will appear in Wellington and Sanders in Auckland.
Dylan John Pyle was also remanded to October 27.
At times during the registrar's list, the group could be heard cheering and chanting outside the courtroom.