A homeless man allegedly whacked a 21-year-old woman with a leather belt in an unprovoked attack outside NBC Studios Tuesday morning, cops said. 

Kamal Walker, 25, came up behind his unsuspecting victim and struck her in the lower back and left arm in front of the network’s building on West 49th Street near Fifth Avenue around 7:45 a.m., authorities said. 

The victim, a Manhattan resident, was treated on scene by EMS. 

Walker was arrested a short time later and charged with two counts of assault, police said. 

The incident came two days after Samuel Poulin, a Marine — also 21 — was hit in the upper back by a ricocheting bullet outside the Marriott Hotel on West 45th Street and Broadway, just blocks away. 

Poulin, who was visiting from upstate Northville, was not the intended target, cops said.