The court was told he'd believed Mr Paterson had meant him harm.
Hickson told police Mr Paterson had arrived at his Edmonton home on November 6 and had started using tarps and fishing nets to enclose the back yard.
"He (Mr Paterson) was making out like he was making it safe ... to me I was getting caged in," Hickson told police.
On the morning of November 7 Hickson said he and Mr Paterson were both in the lounge area and "we both reached for something at the same time and he was slower than I was I guess".
David Hickson is accused of murdering Campbell Paterson.
Hickson said he grabbed a hunting knife with a serrated blade about 40cm in length in total. "I've just reacted," he told police. "It just happened that quick.