A 28-year-old man was found with a knife in his pocket shortly after police received a 999 call about a street robbery.
Officers were called to Crowtree Road in Sunderland after a pedestrian reported he had been approached by a man brandishing a knife and demanding money.
Ryan Richardson was arrested nearby because he matched the description given by the alleged victim, South Northumbria Magistrates' Court heard.
"When police were speaking to Richardson they noticed he was trying to conceal something in his sleeve," said Lesley Burgess, prosecuting.
"That turned out to be a knife blade about 9in long. He was arrested on suspicion of robbery.
"Richardson told officers he had just found the knife blade in the street.
"He said he had picked it up to prevent it falling into the hands of the kids."
Richardson, of Ravenscourt Road, Red House, admitted possession of a bladed article on August 17.
Angus Westgarth, defending, said: "The circumstances of the possession are as Mr Richardson says.
"He found the knife 10 minutes before he was arrested, and he had intended to dispose of it.
"There is no evidence he took part in a robbery.
"Mr Richardson had a difficult upbringing, and he faces further difficulty in the future.
"He could lose his liberty for this offence, but all it amounts to is putting a knife in his pocket and carrying it for 10 minutes.
"The knife was not produced or used in any way."
Richardson was sentenced to eight weeks in prison, suspended for 12 months, including 30 days of rehabilitation activity.
He was ordered to pay £200 costs, and the knife blade was confiscated, and will be destroyed.