NFL's Adam Gotsis Gets Massive, 3-Foot Tattoo Covering Back & Butt

It didn't seem possible ... but NFL defensive lineman Adam Gotsis has found a way to be even more of a badass -- by getting a sick, 3-foot tattoo all over his back and butt!

TMZ Sports has learned the 6-foot-4, Jacksonville Jaguars pass rusher hit up artist JB Tattoos to get an extra-large tat done of a Japanese Hannya mask -- which symbolizes wisdom and good luck.

JB -- who's located in Denver -- tells us Gotsis flew him out to Florida to get the ink done ... and after sketching out the artwork on 9 sheets of paper, the two went to work.

JB says he tatted Gotsis from his neck to his glutes for two, 12-hour sessions within two days ... and tells us the 29-year-old sat like a champ for a tat that ended up covering around 3 feet of his huge frame.

"He was a savage," JB says. "Only minor twitches here and there!"