It happened at the Sports Authority at 1100 Rocky Run Parkway in Wilmington around 5:10 p.m. Tuesday.
Police say the suspects entered the store and removed three pairs of sneakers that were on display, hiding them under their coats.
As they went to leave the store, the security guard tried to stop them.
That's when one of the suspects allegedly pulled a knife on the guard, who then stepped aside and let the trio out of the store.
The bandits then got into a white Chevy Blazer and fled southbound on Route 202.
The security guard was not hurt.
Anyone with information is asked to call police at 302-834-2630 ext. 6 or Delaware Crime Stoppers at 1-800-TIP-3333.
Suspect #1: Black male, 40-45 years of age, 6'00" tall, 210-220 lbs, medium brown complexion, and brown eyes. He was last seen wearing a dark blue coat, light gray sweatshirt, blue jeans, black boots, and a light gray wool cap. He was also armed with a folding pocket knife.
Suspect #2: Black male, 25-35 years of age, 5'08"-5'10" tall, 160-180 lbs, average build, medium brown complexion, with a short black hair. He was last seen wearing a large puffy white winter coat, white t-shirt, blue jeans, and tan boots.
Suspect #3: Black female, 25-35 years of age, 5'05"-5'07" tall, 130-140 lbs, and black braided hair that was pulled back in a pony tail. She was last seen wearing a dark coat, and blue jeans that were ripped at the knees.