Katie Rhee knows she shouldn’t be playing sports, let alone one with heavy contact and no helmet or pads.

A deep muscle strain suffered as a high school diver pushed her spine out of alignment, risking paralysis. She has no more cartilage left in between her tibia, fibula and femur, and around her patella in both knees. And she’s had a concussion.

“I was also told that if I were to continue playing sports as intensely as I do, my body will start to deteriorate at the age of 30,” Rhee, 19, said. “But there’s no way that you can stop me. I’m still stubborn, I’m still going to play.”

Despite the severe injuries Rhee sustained before college, she decided to pick up Australian rules football. Last weekend, the Emerson sophomore competed in the United States Australian Football League national tournament just six months after her first practice.

Rhee was first introduced to the game during her freshman orientation week at Emerson. She was sitting on a couch in the eighth floor common room of Little Building with a friend when she spotted a tall man walk past the room and down the hallway. Suddenly he ran back to the room and, standing in the doorway, said to her: “Are you Katie Rhee? I’m your mentor. I’m John Newton.”

Newton was a sophomore at the time and had been paired with Rhee as part of a mentorship through the school’s journalism department. He was featured as an Australian football player in a Beacon article last year.

After their first meeting, an awkward one the two said, Newton showed her the YouTube video he shows everyone: a five-minute instructional on how the sport is played in the prominent Australian Football League.

“I can’t tell you how many dozens of people I’ve showed that video to,” Newton said. “People who don’t know what the sport is have no attention span for it. So I really have to sell it while they’re watching the video.”

Rhee wasn’t convinced, but she spent a lot of time with Newton and Olin Hayes, another Australian football player, in the following months. She streamed many games with them, and it began to pique her interest.

Rhee said she was in a dark place last March and had no motivation to live. She decided to join the Boston Lady Demons in a last-ditch effort to change that.

The Demons have a women’s and men’s team, the latter for which Newton has played over the last three years.

Her first practice was at eight o’clock on a frigid morning. She showed up to the field with jewelry and long fingernails, which she soon broke.

Walking off the field with bruises and bumps on her feet and ankles, and several jammed fingers, she was hooked.

“I thought I was doing terribly, but everyone told me I was a natural,” Rhee said. “I was like, ‘Are you kidding me?’”

She made excuses for not giving it her all in games in the early going, Newton said, worrying about her knees and especially her back, where she used to feel pain bending over to wash conditioner out of her hair. Other days, she couldn’t get out of bed.

But the aches were minimal when she joined the Demons, and as she continued to play and learn more about her newfound passion, she gained confidence. She became aggressive and is now called a “tackle-happy” forward by her teammates.

In hockey and lacrosse, men’s teams have more freedom in physical contact than women’s. In Australian football, there are no such rules.

Rhee said when she sees an opponent with the ball, she sprints straight to them to make a tackle.

“I’ve seen her start to pare down her excuses through this sport,” Newton said. “It’s also changed her life in a way where she’s just got a more positive attitude. Mentally, she’s in a happier, better place. More confident in herself, for sure.”

When Rhee first started Australian football, she said her parents were not thrilled, given her injury history. But she said they and her friends understand why she does it, even if they don’t understand what she does.

Rhee had no plans of going to nationals this fall, and said she even declined an invitation from the Boston Demons chairman. She was roped into it when the chairman later demanded she say yes, without asking a question. Rhee, believing it to be unrelated, said yes, and he followed her answer by saying, “Cool, I’ll see you in October.”

Eight members of the Demons, including Rhee, played for the Baltimore-Washington Lady Eagles as a joint team at the event in San Diego. They finished 1-3 and fourth out of five squads in the second women’s division, earning a shutout in their lone victory.

Rhee and Newton say they have a special relationship. More than just great friends, they’re also teammates. They make sure each other eat right and drink a lot of water. They train together outside of practice, and now, when Rhee watches those streamed games, she studies the plays and has Newton break them down for her.

“You don’t really have that raw relationship with other people,” Rhee said. “I have John, and I know that he’ll hold me accountable, and I hope he knows that I do the same for him.”

Newton said he wants to help her go far.

“She’s told me what she wants to accomplish, so it’s up to me, as her teammate, to help her get there and do everything in my power to help her get to where she wants to go,” Newton said.