Robert Sheppard, 41, of no fixed address, has been sentenced to a total of 20 months in prison after police were called to the incident on Monday 4 September at Sports Direct in North Street.
He stole two pairs of joggers worth £159 each and proceeded to threaten staff with a knife.
Police acted swiftly and with thanks to a member of the public, arrested him just a few minutes later, despite Sheppard trying to get away.
Sheppard pleaded guilty to possession of a knife, threatening with a knife, and theft from a shop, and appeared at Lewes Crown Court on Tuesday 4 October for sentencing.
He was also ordered to pay a £187 fine and given a 24-month Serious Violence Reduction Order (SVRO), the first of its kind in West Sussex.
Police now have the right to search Sheppard in a public place to check he isn’t carrying an offensive weapon, under the order that runs for two years.
Sergeant Sam Milsom said: “Sheppard is a dangerous individual who carries knives upon himself, having no regard to public safety.
“This is a terrifying ordeal and not something that anyone who goes to work would expect to deal with.
“Sheppard has rightly received a custodial sentence and will be subject to a SVRO when released from custody.
“I would like to thank the member of the public who aided police that day in apprehending Sheppard as he fled from officers. It’s people like them who help police lock away violent and dangerous offenders.”
