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The threats were made last year by a New Zealand fan and were serious enough for the Australian Federal Police to contact local authorities in advance of Plummer travelling to Dunedin with her West Coast Fever side for the weekend's transtasman league game against the Southern Steel.
The Fever said last night that the threats were made via a posting on Plummer's personal website.
The New Zealand Herald understands Plummer was so shaken up by the sinister tone that the team beefed up security during their stay down south.
The team and support staff left the stadium swiftly after their one-goal loss to the Steel on Saturday, missing a post-match function.
Police Southern District confirmed information had been received from the Australian authorities but would not comment on the investigation.
Plummer did not wish to comment on the incident and a spokeswoman for the franchise said the veteran coach "just wants to do her job".
The Fever team are now in Tauranga as they prepare for Sunday's round five match against the unbeaten Waikato-Bay of Plenty Magic.
Steel chief executive Sue Clarke said the franchise was not made aware of the Fever camp's concerns in the lead-up to the weekend's game.
"We would be very disappointed to learn of any visiting coach or team being treated in a negative way," she said.
Known for her outspoken style, Plummer has often courted controversy over her coaching career.
She got off to a rocky start with New Zealand fans when, after taking on the Australian coaching job, she famously claimed the Silver Ferns played like a "bunch of scrubbers" in the 2003 world championship final.
While her frank and forthright approach has often jarred with the conservative netball set, many consider Plummer to be a breath of fresh air for the controversy-shy sport.