Detectives also uncovered evidence of drug supplying and money laundering, but these offences did not relate directly to the NRL.
The investigators will not lay charges for any of the illegal practices uncovered, but they have referred matters to other members of the Organised Crime Squad and the financial intelligence regulator AUSTRAC for further investigation.
"While detectives have not preferred criminal charges relating to these issues, their investigation highlighted activities and practices that are deemed as high risk for the NRL," NSW Police said in a statement.
"In light of this information, representatives of Strike Force Nuralda have recently met with the NRL and provided recommendations to ensure the integrity of the code is not compromised by the infiltration of organised crime."
The inquiry was sparked in October 2015, when police received allegations of illegal gambling and match-fixing within the NRL.
Investigations stepped up a gear after the NRL and betting agencies referred on evidence of suspicious betting on a match between Parramatta and Manly in April 2016.
Since then, police have examined 46,000 pages of betting data, 300 pages of data from AUSTRAC and more than 1000 pages of telecommunications data.
Detectives identified 13 potential persons of interest and spoke with 161 witnesses including players, referees, NRL staff, professional punters and associates of the persons of interest.
Some players were interrogated in secret statutory hearings undertaken by the NSW Crime Commission.
The strike force found punters - including players and former players - who would normally bet about $50 on a game were wagering up to $15,000, The Daily Telegraph reports.
Police have not named any of the players involved in any of the suspected criminal acts.
The investigation also looked at the practice ofpoint shaving - where strong teams or significant players within teams who are expected to win by big margins, pull back to only win by small margins - but it did not find that it had occurred.