“NBA referee” is among one of the most unforgiving professions in the world, as one minor mistakes could suddenly be criticized by thousands of fans in an arena and millions who are watching in their TV set.

Yet a chosen few get to make it into the league with one warning — it is not for the faint of heart, or the thin-skinned.

Refs are often the number-one target of criticism in an NBA arena, as insults and middle fingers fly free and often through the course of a game.

Per ESPN's Jackie MacMullan:

“Before you get hired,” referee Mark Davis explained, “they take a body scan, and right below your heart there's a little vacuous spot. That's where your feelings go. If it's empty there, then you are an NBA ref.”

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NBA refs have been enduring abuse since the start of the sport, and as ticket prices skyrocket and the stakes get higher, the abuse gets only worse.

Dr. Joel Fish, a sports psychologist and director of the Center for Sport Psychology in Philadelphia, has worked closely with NBA referees and knows just how the unique setting of their workplace can have a cumulative stress that can have short- and long-term implications.

“We're not talking about the kind of stress that goes away after a good night's sleep,” Fish said.

“These people are humans, not robots,” he added. “They have feelings. So we work on identifying what might set them off and how they can avoid that from happening. It's almost like a rehearsal, so when they are challenged, it's nothing they haven't anticipated.”

While refs have to be in tip-top shape to officiate NBA games (lets remember, they are the only players who actually run all 48 minutes of regulation), they also have to put their minds in the zone, not only to make judgment calls, but to prepare to face the ensuing abuse from players, coaches, and worst of all — the fans.