Here's a bit of an insight on what happened....also he was not working with the stingrays for his "Oceans Dealiest" show.
Irwin, 44, was killed by a stingray barb that pierced his chest, according to Cairns police sources.
Irwin was in the area to film pieces for a show called "Ocean's Deadliest" with Phillippe Cousteau, grandson of Jacques, Irwin's manager and friend John Stainton told CNN's "American Morning." But weather had prevented the crew from doing work for that program, said Stainton, so Irwin decided to do some softer features for a new children's TV show he was doing with his daughter, Bindi.
"He came over the top of a stingray that was buried in the sand, and the barb came up and hit him in the chest," said Stainton.
Wildlife documentary maker Ben Cropp, citing a colleague who saw footage of the attack, told TIME that Irwin had accidently boxed the animal in, causing it to attack. "It stopped and twisted and threw up its tail with the spike, and it caught him in the chest," said Cropp. "It's a defensive thing. It's like being stabbed with a dirty dagger."
http://www.cnn.com/2006/SHOWBIZ/TV/09/04/australia.irwin/index.html