One of Hollywood's most outspoken liberals is getting a crash course in media bias.

Only Mark Ruffalo isn’t complaining about the media’s incessant cheerleading for the left. Instead, the man who plays The Hulk in the “Avengers” franchise is furious at how reporters are treating Sen. Bernie Sanders.

Or, in too many cases, not treating him.

Mainstream news outlets aren’t giving the Sanders campaign the attention, and credit, it deserves. And Ruffalo is right, of course. But it’s much more complicated than that.

Ruffalo just released a new video throwing his celebrity weight behind Sanders, the Socialist Democrat from Vermont. It calls for a “ReLoveLution,” or something like that.

The actor isn’t just cutting videos for Sanders. He’s aggressively challenging the media status quo.

Ruffalo complained to Variety this week that Sanders isn’t getting much media traction. Part of the problem can be attributed to Donald Trump, the actor says. The real estate mogul dominates the news, leaving less air time for Sanders or anyone else.

That doesn’t make it right.

So Ruffalo used his journalism connections, honed during his time making the Oscar-winning film “Spotlight,” to find some answers.

He got little relief from the heroes behind that fact-based film.

“They just basically say that Trump has sucked all the air out of the room,” Ruffalo says. “But no matter what it is, it has to stop.”

That’s not how media bias works.

What Ruffalo doesn’t grasp is that media bias isn’t a 2016 problem or one solely affecting the Sanders campaign. It’s been going on for some time. But since the scales have been tipped in his side’s favor, he hasn’t said much about it.

Consider:

Why? Liberal media bias plays a major role, no doubt. Roughly half the country understands the press works on behalf of liberal causes and politicians, and it shows in their coverage.

Ruffalo isn’t angry about that cold, hard reality. He should be. And as soon as he starts turning green about it, he’ll bring more credibility to the media bias conversation.