Natan Levy says his recent beatdown of an internet troll could have been much, much more violent ... but he tells TMZ Sports he let his foot off the gas just a little bit so the guy still had "some brain left to take the lesson in."
The UFC fighter, who's Jewish, sparred the smack-talking social media user, Ben, a few days ago ... after the guy defended noted antisemite Nick Fuentes in an exchange on X.
Ben met up with Levy at his gym in Las Vegas ... and after Levy had explained why he was so furious at Ben for supporting Fuentes -- a man who the Anti-Defamation League has called "a white supremacist leader" -- the two threw on gear and stepped into the cage.
Not long after, Levy destroyed the guy.
But, Levy said it could've been worse ... explaining to us he could've sent the dude home in an ambulance -- but he held back.
"It wasn't easy," Levy said of holding back, "but again, great power comes with great responsibility and I wanted to teach him a lesson."
Seems it was effective nonetheless ... as Ben went on camera following the sparring sesh and acknowledged that six million people were murdered in the Holocaust.
As for what's next for Levy ... he'll take a break from beating up online bullies next month to try and take down Alex Reyes during their tilt in Vegas on Sept. 16.