Her book 'Night Games: Sex, Power and a Journey into the Dark Heart of Sport', about the rape trial of a young Australian Rules footballer, beat six other nominees to the 26,000 pounds (USD 40,879) prize including the autobiography of former Wales and British Lions rugby player Gareth Thomas.
Krien, who matched Laura Hillenbrand's 2001 feat for 'Seabiscuit: The True Story of Three Men and a Racehorse', said on Thursday that the tough subject matter made it a brave choice for the judges.
"It's not a celebratory book about sport," she said, adding, "It's about the dark side of sport...it can be pretty ugly."
The judges described the book as a "balanced yet fearless" exploration of the behaviour of sportsmen and their treatment of women and it was an essential, if uncomfortable, read.
Krien, who had a child while writing the book, described the task as more labour intensive than a labour of love and said she had to overcome much opposition from people involved in the sport.
"There was the obvious opposition from the football fraternity saying, 'Don't go there, this is something we don't talk about'," she added.
"Many mainstream sports writers that I tried to interview also cut me off because they didn't think I had the right to write the book," said Krien, referring to her lack of a sporting background.
"It was very much a turf war," she said.
So what drove the author to continue with the book?
"The importance of the subject," said Krien.

“I wanted to open the debate but I didn't want to close it. I think it needs more people to get involved and talk about it," she added.
Although the book is about Australian Rules, Krien said the book should resonate throughout sport.
"Sport is a great lens to look at issues other than just the spectacle in front of your eyes," she explained.
"Being a sportsman is not a normal occupation. You're a role model whether you like it or not. What you do matters on and off the field," Krien added.

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