The detective witnessed the incident at about 12:15 p.m. ET and chased the suspect.
Deshawn Quinton Johnson, 26, of Baltimore, was arrested and charged with robbery, theft, resisting arrest and reckless endangerment.
The 51-year-old victim, a loss prevention officer at an Office Depot on Ritchie Highway, saw Johnson try to leave the store with stolen goods.
The victim then confronted Johnson and began dialing 911, at which point Johnson shoved the man and took his phone.