It all happened behind a locked door as Santamaria returned home to her apartment complex at Westmoreland Avenue and 11th Street around 10:10 p.m. Sunday.
"That's where I walked in, and I felt him behind me, and I was like 'Woah!' and that's when it happened," said the 18-year-old.
That beating was all captured on surveillance camera.
"When he dropped me I didn't expect it, I was so caught off guard so much, I was just like, 'Woah,'" she described.
Barely 4 feet 11 inches tall, Santamaria fought back.
"I snapped into this mode where I was like boom, boom. I was trying to defend myself," said Santamaria.
The suspect beat her again. She tried to stop him from leaving, but he escaped with the cellphone in hand.
Eventually, neighbors heard Santamaria's screams, but it was too late.
She suffered some bruising to her face, but refused medical attention, police said.
Police released surveillance video of the incident and are asking for the public's help to identify the suspect. He is described as a Hispanic male, between 25 to 35 years of age, 5 feet 5 inches tall and about 180 to 200 pounds. He was last seen wearing jeans, a white T-shirt with black printing on the front and back and black shoes.
If you have any information regarding this case, you're urged to call (877) LAPD-24-7.