The metal blades were spotted by security in the man's carry-on bag as it passed through an X-ray machine, and the man was stopped as Maryland Transportation Authority Police officers responded, the TSA said.
Officers found the blades only after every item in the man's bag was removed and X-rayed separately, which revealed the blades inside of a "well-worn," orange-and-grey New Balance running shoe, the TSA said.
The TSA described the blades, which are prohibited, as "two pieces of box cutter-type blades," and said police had to "tear open" the shoe to retrieve them.
"During the police investigation, it was determined that the blades appeared to have been manufactured into the sole of the shoe for the right foot," the TSA said in a statement. "The passenger was permitted to catch his flight."
The man was not arrested or issued a criminal citation.
"There have been many instances in which people try to intentionally conceal blades in their shoes," said Lisa Farbstein, a TSA spokeswoman, in a statement. "However after the investigation, it was not believed to be the case in this instance. The belief is that somehow the blades found their way into the shoe during the manufacturing process."
First Sgt. Jonathan Green, a MdTA Police spokesman, said investigators determined the metal in the shoe — which he said more resembled "a couple rusty pieces of sheet metal" — was a "manufacturing defect."
Amy Dow, a spokeswoman for New Balance, declined to comment Thursday afternoon, saying the company was still gathering information about the incident.