NFL Combine: Players Get Sick Custom Cleats ... On the Spot!

Some of the best cleat customizers on the planet are at the NFL Combine -- banging out personalized cleats for any player who wants 'em ... and it's all free!

TMZ Sports has learned ... Under Armour hooked up with the guys from Dez Customz and Kreative Customs to pimp out their footwear as a special treat for the players at the combine.

The guys literally have hundreds of pairs of cleats -- and players come into the room at the hotel, select their shoes, tell the guys what they want ... and the artists go to work.

We're told some of the requests have been for comic book characters like the Hulk and Batman ... some have asked for school colors ... and others have just said, "make something cool."

And despite the fact they usually take hours to make ... the artists are knocking out dozens of KILLER DESIGNS in record time for some of the top players in the country.