A Stars fan was socked in the face by a huge haymaker at Dallas' game on Wednesday night ... with the massive punch coming after the guy said the n-word.
The altercation went down just a few seats from the American Airlines Center ice ... when a man in a Jamie Benn jersey stopped watching the Stars vs. Wild tilt -- and began jawing with another fan behind him.
No word on why their beef initially began -- but the dude in the green No. 14 uni was clearly furious. At one point, he challenged the other fan to a fight .