Undefeated MMA fighter Dustin Lampros has made a name for himself in the cage, but he's also fighting to get child predators off the streets -- and he's telling TMZ Sports the wildest interactions he's had while trying to make that happen.

We caught up with 9-0 Lampros ahead of his Shamrock FC title fight on March 22 ... and he opened up on how he started his meaningful side gig with a friend two years ago to make a difference in his hometown.

"When he exposed it to me and brought me into that world, I instantly felt motivated to do something," he said. "I looked at him right away and said, 'Let's do it, let's help down here in the community.'"

"At first, it was kind of like, 'let's see what we can do.' Then it kind of snowballed from there."

In terms of total captures ... he thinks they are around the 50 mark. While the 30-year-old has never gotten physical with anyone, he has had some weapons pulled on him.

"A kid pulled out a little box-cutter knife, and he's just holding it in his hand, and then we didn't notice it until about 20-30 seconds later," Lampros said.

"I've had one time where a guy wouldn't talk to me, and he just walked back to his car, and he said, 'You better not follow me to my car,'" he said. "I had a hunch he was going to grab something, and he did. He grabbed a handgun."

Luckily, nothing ever came of those encounters ... but Lampros said they take all the precautions when they put themselves in these situations.