The tunnel before a World Cup match is a busy place. Players stretch and move to work through their nerves. Children assemble to walk on the field with their heroes. Cameramen snap pictures.

And then, in the middle of it all, there’s sometimes a voyeuristic game official asking the players to lift their shorts, like this linesman did before Monday’s Panama-Belgium match.

It’s not an uncommon sight if you watch enough soccer matches, but even some of the most devout fans might be confused over what the official is looking for.

Foreign substances? A billy club? A sandwich for mid-match snacking?

The answer, though, is somewhat boring. The official is simply checking to make sure the color of the player’s undershorts (if he’s wearing any) match the color of his regular shorts. FIFA rules explicitly state that any undershirts or undershorts must be the same color as the kit’s top layer.

Other federations have the same rule. Denmark’s Nicklas Bendtner was fined during Euro 2012 for displaying green undershorts that promoted a betting company.

The company, Paddy Power, picked up the tab for Bendtner’s fine.

In 2011, Bath City had five players sent off from a FA Youth Cup match for non-matching undershorts after officials failed to check before the game.

What happens if the official finds something clashing is unclear, though it’s likely the player is simply asked to conform with the rules before entering the pitch.

Better to change their shorts back in the locker room, of course, rather than in front of an entire stadium.

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