Mr Pratt was one of nearly 100 people arrested over the weekend in the city, but only 14 of these arrests took place at the Westpac Stadium.
Last year, 44 of the 105 arrests were at the stadium. In 2010, police arrested 113 people, 42 of which were at the games.
Event organisers earlier this week apologised for the breach of security which allowed Mr Pratt to reach Tupou.
"We take this breach of security extremely seriously. It is not acceptable to put players in that position," Hertz Sevens General Manager, Steve Walters said.
"We regret the incident and are disappointed that one person's actions detracted from an otherwise good first day. The offender has been charged with assault."
"Wellington has built a reputation for hosting international sporting events and this mindless act jeopardises the tournament's world class standing."
- NZ Herald Online staff