"I could see right into my scrotum."

That's probably the last thing you wanna say after a pole vault training sesh ... but it's exactly how BYU athlete Zach McWhorter is describing his pole vs. balls injury.

The 21-year-old was having a pretty typical training session at the BYU track -- recording it to post on TikTok -- when disaster struck.

At first, it seemed like a standard jump ... but McWhorter's pole didn't fall the way it supposed to and essentially impaled his scrotum.

YOWWWCH.

McWhorter told BuzzFeed he was immediately rushed to the hospital by his dad/coach/urologist ... where he needed 18 STITCHES to get patched up.

Luckily, the dude says he only has a scar from the incident. As for any permanent damage, McWhorter says "One day, we'll find out if they function or not."

Ice up, Zach. And, maybe wear a cup from now on??