Young children through to the old were spotted joining in the dress-up fun.
One man, Mo Mackey, had brought his 7-year-old son Breyton along to experience today's tournament.
Breyton had picked out their matching robbers outfits, but he said he hadn't yet decided which team to support.
Mr Mackey's partner and daughter would be attending tomorrow's section of the tournament. The experience was a christmas present for their children, Mr Mackey said.
A group of six ninjas, originally from England, Wales and North Ireland, but living in Auckland, had made their way to Wellington for their first sevens experience.
One of the ninjas said she was very excited, but was worried her costume might get too hot.
A plan to get supporters to the tournament early has seen Museum Hotel put up $25,000 in prize money for costumes.
Individuals and groups could enter a catwalk competition from 12.30 to 2.30pm today and tomorrow.
The winner would be announced on the field on Saturday evening.
Tickets for this weekend's tournament sold out within three minutes late last year.
The final game would be played at 9.30pm on Saturday.