Sydney Sweeney on 'Sports Illustrated' Cover With Christy Martin

Sydney Sweeney graced the cover of the latest issue of "Sports Illustrated" ... where she posed with Christy Martin and dished on playing the renowned boxer in the new biopic.

According to Sweeney, "Christy" is the "most important film" she's ever made.

In an Instagram post Tuesday, she said, "For 20 years, Christy Martin was one of the strongest women in the world inside the ring. But at home, she was abused and nearly killed by the man who claimed to love her."

She added that Christy's story isn't just about boxing ... "It’s about identity, survival, and the unimaginable strength it takes to reclaim your life after someone has taken everything from you."

For Sweeney, the film isn't just about getting awards or money, but reaching the victims of domestic abuse who feel helpless and unseen.

"We’re here to stand with survivors," she wrote. "And if this film helps even one person feel seen, understood, or less alone, then we’ve done something that matters."

In her interview with 'SI,' Sweeney reveals ... from an acting perspective the role was also attractive to her. It presented the unique challenge of playing a character who is herself, at times, playing a character.

Sweeney said, “The perception is that the media version of who you are is who you actually are.”

She vented that people get "a lot of things" wrong about her -- but didn't go into detail about what those things might be.