John A. Nelson, 20, of 1238 Sycamore Avenue, was arrested after the incident early Sunday morning.
It was around 1:00 a.m. when, police say, they responded to a large party across from the Aetna Fire Station in Newark, Delaware.
That's when officers say they heard screams for help from the back of the home. That's where they found the victim, a 17-year-old girl, on the ground below a 2nd floor window being helped by several other people.
Police say they learned the victim was alone in a locked 2nd floor bedroom when Nelson, an acquaintance, kicked in the door.
The girl tried to flee, police say, and that's when Nelson allegedly grabbed her by the throat and choked her into unconsciousness.
Police say Nelson then sexually assaulted her and, after the assault, threw her from the bedroom window.
The victim remains at Christiana Hospital with injuries including a broken arm and a punctured lung.
Nelson was arrested at his home without incident.