I had just finished performing at the Three broomsticks on the evening in question when Rosmerta and a rather scruffy looking bloke stepped onto the stairway, having a heated argument. Seamus Finnigan, one of the bouncers, stepped over to break up the argument when the bloke took a swing and punched Seamus in the nose. Before I could assist, the bloke left the 3Brooms with a small boy. Rosmerta helped Seamus into the back to heal his nose, and everyone went back to their seats. There was no further incident after that.
I do not know what they were arguing about or why. Everything happened too fast for me to hear.
I hope this helps with your investigation. Please contact me if you have any questions.