David Harbour Takes a Guy's Hat in Bizarre Bar Incident

David Harbour was captured on video doing some "Stranger Things" in Encinitas, California over the weekend ... the actor appeared to take a man's hat and make a run for it.

The head-scratching incident appears to have gone down Saturday at a gastropub called Encinitas Ale House.

Here's what the video -- which we were only permitted to view -- shows ... David enters the joint and then -- a short time later -- runs outside, carrying a white cap in his hand. He then looks over his shoulder, yelling, "C'mon, dude, f****** get me."

Then a patron appears to walk after him, putting his hands up in exasperation and saying, "What the f*** did I do to you, dude?" Moments later, a bunch of people -- who seem to know the man missing his hat -- filed out of the bar to see what was going on.

Then a woman's voice can be heard pleading, "Don't get into a fight!," as the man eventually returns to the bar with his hat. We're told nothing got physical between the two and they went their separate ways.

TMZ spoke to an eyewitness at the bar who tells us... David walked by the bar with a friend, and the guy with the hat ran out to say hello to him. We’re told David's friend told the guy they were meeting up with some girls, but then David said, "No, let's go to this guy's house."

Our source says this struck the guy as strange, so he returned back inside the bar. Shortly later, we’re told David entered the bar, took his hat and fled. The witness says David spiked his hat on the ground and asked the group about the Iraq War, then began to get emotional before kneeling down to pray.

We reached out to rep for David for his side of things... so far no word back.

However, a source with direct knowledge tells TMZ ... "David has always been honest about managing his bipolar disorder. Wouldn’t be surprised if that’s what he’s dealing with here after working non-stop all year and having his personal life under public scrutiny. That would be stressful for anyone but even more so for someone who is bipolar."

David himself has candidly discussed being diagnosed with bipolar disorder in the past.

This comes after the "Stranger Things" actor had been under fire for a report claiming his costar Millie Bobby Brown filed a bullying and harassment complaint against him while filming the final season of the Netflix show. Executive producer Shawn Levy and Millie herself have come out and categorically denied those claims.