What turned out to be a 1,400 pound, 14-foot-long tiger shark took a 16-inch bite out of her surfboard, and Hamilton nearly died from loss of blood.
"When I first saw her in the hospital that morning, she looked really pale, but she had a brightness in her eyes that I could just say, 'You know, she's going to be all right,'" Hamilton's mother, Sherry Hamilton, told ESPN at the time.
In "Soul Surfer," Sherry Hamilton is played by actress Helen Hunt of TV's "Mad About You" fame, and Bethany's father, Tom Hamilton, is played by actor Dennis Quaid.
There are a few elements of fiction in "Soul Surfer," though, such as Hamilton's potential love interest.
"I don't have a boyfriend," she said. "Life's pretty hectic right now, and I'm not really in a rush. I'm really just excited to save my purity for marriage, and I'm not really hunting down any one person but just enjoying life."
At the time of the attack, many doubted if Hamilton could ever surf competitively again, but she just back into the water only a month later and pushed through it. She earned the silver medal at the Billabong ASP 2009 World Junior Pro championships.
Hamilton once described surfing with one arm as similar to doing a "one arm pushup."
"I'm pretty used to it," Hamilton said. "I forget what it used to be like" to have two arms.
But when she first returned to surfing, Hamilton had to relearn a sport that had become second nature.
"I kind of struggled on my first couple of waves and didn't get up," she said. "I got up on my third wave and road it all the way to the beach. I was just so stoked, just had this joy feeling inside me."
To help her paddle out to the waves, her father came up with the idea of putting a handle on her board so she could catch her balance.
"Every time I would go out there, I would learn something new," she said. "I kept practicing just on smaller waves, just standing up and figuring out how to catch it and all that and each time I felt better and better about my surfing."
It's no wonder that Hamilton's biggest challenge and the incident that propelled her to national fame happened in the water. Born into a family of surfers, Hamilton had been catching waves and trophies since the age of 8.
Hamilton had drawn as much admiration from her community after the attack as she had before. Many have called her a role model, although she said she doesn't feel like one.
"I'm still surfing and loving life and being able to reach people a lot more than I would have, probably, with two arms," she said.
Her positive attitude won her a 2004 ESPY Award from ESPN for Best Comeback Athlete of the Year and a special Teen Courage Award. She's now ranked among the top 10 professional women surfers in the world.
On top of physical hurdles, Hamilton has overcome psychological ones too, namely, the fear of another attack.
"You never know" if it could happen again, she said. "When I'm feeling scared I just sing a song or pray ... or [I] just try to ignore it and, you know like, it's always in my mind."
"I just do my best to be smart about when and where I surf," she said. "I don't go out if it's questionable. And when I'm out, I head in if I get scared or think I see a shark."
Over time, Hamilton became comfortable with her physical disability. Early on, she had a prosthetic arm custom made for her but chose not to use it.