Derrick Lewis was caught on video delivering a body shot to a willing fan in a clip that went viral on social media, with the recipient appearing to drop immediately before eventually getting back to his feet to a round of laughter.
The video was posted by former UFC fighter Mana Martinez, with the caption suggesting the punch may have been a birthday gift of sorts.
Lewis appeared to take something off the shot, but it was still enough to drop the man, who needed assistance standing and could be heard laboring to catch his breath as laughter erupted off-screen.
Lewis faces Josh Hokit at UFC Freedom 250 on June 14 at the White House in what will be a considerably stiffer challenge. Hokit is undefeated and was personally added to the card at the request of President Donald Trump.