Claressa Shields vs. Christina Hammer fight prediction, start time, odds, watch Showtime boxing, live stream. As the first two-time Olympic gold medalist in United States amateur boxing history, Claressa Shields has never been one to pull any punches when talking about her own greatness inside the ring.

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Shields (8-0, 2 KOs), the unified middleweight champion, began openly referring to herself as the best pound-for-pound fighter in the sport not long after turning pro in 2016. After employing a dare-to-be-great matchmaking strategy which included winning her first world title in her fourth pro fight and unifying titles in a second weight class just one year later, the 24-year-old Shields soon began calling herself the greatest female fighter of all time.

So it's hard to consider it hyperbole when the brash native of Flint, Michigan, calls Saturday's middleweight unification bout against Christina Hammer (24-0, 11 KOs) at Boardwalk Hall in Atlantic City, New Jersey (Showtime, 9:10 p.m. ET), the biggest women's fight in history.

"I think it's the biggest women's boxing match to date because you know who both of us are," Shields told CBS Sports' State of Combat last week. "Just the flame that women's boxing has with me being in the Olympics twice, me winning world titles and becoming the first woman to main event on Showtime on premium cable and me fighting on HBO and DAZN co-main events, it just shows how much women's boxing has grown.

"It's not a disrespect to any other fights that Laila Ali had or Christy Martin, Lucia Rijker or Ann Wolfe, but when they fought, you really didn't know who their opponents were. I think with this fight you have two women who are greatly known and then you have a champion who has been reigning from eight years across the way and we are fighting each other for all of the belts."

In Shields' favor are the historic elements associated with this fight. Not only will an undisputed middleweight champion be crowned for the first time but the winner will join current welterweight champion Cecilia Braekhus as just the second women's undisputed champion -- and sixth overall alongside Bernard Hopkins, Jermain Taylor, Terence Crawford and Oleksandr Usyk -- in the four-belt era. The fight has also received tremendous promotion from Showtime which included a two-part "All Access" documentary series following around both fighters during training camp.

The rivalry between the two fighters first gained steam in 2017 following Shields' title win over Nikki Adler when Hammer entered the ring to exchange words and hype a future fight between the two. Then, a second and much more heated exchange complete with shoving took place after Shields got up from the deck to outpoint Hanna Gabriels last June which only fueled the beef between them even more.

At last month's press conference to announce the bout, the 28-year-old Hammer said she has nothing personal against Shields and that the talk between them was strictly professional. It's a claim from that Shields believes just isn't true.

"She's lying. She's talking about how she doesn't have anything against me personally. Big, fat liar. Period. She's lying," Shields said. "She had something against me because she knows I boxed better than her and got more recognition than her and she doesn't like that, along with a couple of other women who thought they should have been getting the recognition Claressa's getting but they haven't accomplished nowhere near what I've accomplished just in my 24 years of life.

"[Hammer] carries that with her and she's upset now that I'm the favorite to win even though she has been the reigning champion for eight years. Of course she doesn't like me, but she can say whatever she wants to say to the media, but I already know for a fact she doesn't like me. That's why she said we could never be friends. Well, I don't want to be your God damn friend anyway. I don't care."