Stuart helped catapult the Raiders into the top four before they lost the grand final to the Roosters and Hasler rejuvenated Manly in his first season back on the northern beaches. Arthur dragged the Eels from the wooden spoon the previous season into the second week of the finals.
But several bookmakers reported a flood of money for Bellamy to win the award and later relayed concerns to the NRL, which in turn passed it onto police.
The award was already tinged with controversy after the NRL’s official Twitter account inadvertently announced Bellamy as the Dally M Coach of the Year about 20 minutes before he was announced at the Hordern Pavilion.
The tweet was quickly removed, but not before eagle-eyed users found out the winner.
There is no suggestion the social media gaffe contributed to the betting anomalies given markets are shut down long in advance of the awards ceremony starting.
The NRL was contacted for comment.
Bellamy used his speech after winning the Dally M Coach of the Year, the fifth time he has claimed the honour, to raise serious concerns about whether Storm skipper Cameron Smith would retire after Melbourne’s preliminary final loss to the Roosters.
Smith decided weeks later he would again play in 2020 and has even left the door ajar for a further season in 2021.
Bellamy also collected Smith’s Captain of the Year award for his absent talisman.
Roosters star James Tedesco was crowned the game’s best player last season when he picked up his first Dally M honour. The Australian and NSW No.1 has opened as favourite to win this year’s gong too.
Meanwhile, global betting exchange Betfair on Wednesday night was yet to sign the NRL’s official integrity agreement just 24 hours out from the start of the season.
The NRL has been locked in a stalemate with some of Australia’s biggest wagering companies in recent months over gambling taxes.
The majority of bookmakers have since struck a compromise with the NRL to allow betting on the regular season, starting with the Eels-Bulldogs blockbuster at Bankwest Stadium.
They will still be subject to a super tax on all State of Origin and finals matches, some of the biggest wagering events in Australian sport.
But having announced it would not offer the chance for punters to match bets on pre-season matches until a “fair agreement” had been struck, Betfair was not offering any NRL product on its website on the eve of the season opener.
The NRL recorded a $30 million profit for its last financial term, with a strong focus on non-broadcast revenue, highlighted by the success of a State of Origin match in Perth, Magic Round in Brisbane and uplift in gambling revenue.
Adam Pengilly is a Sports reporter for The Sydney Morning Herald.