Fans of the Power Slap League were left stunned after watching what they are calling 'the most brutal' knockout in the promotion's history.
Power Slap was founded in 2022 by UFC president Dana White, and is contested over three rounds.
In each round, one fighter is given 60 seconds to hit their opponent with an open-handed slap below the eye but above the chin, with the roles then reversed.
The sport in general has received significant criticism from brain injury experts, with the impact of the hits compounded further by the fact that competitors are not allowed to flinch, duck their heads or wear headgear.
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One male fighter suffered a brain bleed after a slap-fighting knockout in 2021 - a year before the Power Slap League was founded - and later died.
While a female fighter lost consciousness twice during a slap fight two years later.
But fans think they've seen the promotion's worst-ever knockout - in footage that left even ex-UFC and WWE star Ronda Rousey stunned.
In the clip, one Power Slap fighter is struck clean on the side of the head, knocking him out instantly.
His head then crashes against the platform below him and he falls motionless towards the ground before being caught by two on-site medical staff.
Warning: The below footage contains scenes that some viewers may find distressing.
In response, fans have voiced their concerns.
One wrote: "This seems insane. It's just first to give the other a concussion wins. I really don't get it."
A second added: "This s**t should not be sanctioned."
A third agreed: "Guaranteed CTE every round. How in the f**k is this legal?"
And a fourth added: "Guys I don't think I can continue to support this sport."
Several high-profile names from the world of combat sports have competed in Power Slap, including former MMA fighter Paige VanZant.
Meanwhile, Shotzi Blackheart, who was released by WWE last month, revealed that she was approached to take part but declined the offer.
Topics: Ronda Rousey, Dana White
Ryan Smart