Why are men singing at night in Madrid

I've mentioned in earlier entries the noise that is more or less constant from 4 p.m. to 4 a.m. Most of it comes from customers of the bars and restaurants nearby, from other pedestrians, from garbage trucks, and from drivers honking their horns at the garbage or delivery trucks blocking the street.

But I'm only about 100 ft. from Gran Vía, a major east-west street with many large stores, sort of the equivalent of Michigan Avenue shopping district in Chicago -- or the way Michigan Avenue used to be in the past, I don't know how busy it is anymore. Also quite near on Gran Vía is a major subway station and a large plaza. Suffice to say thousands of people pass by or gather there every day, sometimes pausing to appreciate the break dancers who nightly put on a show in the plaza. So from noon, say, to at least midnight, I can easily hear a constant low-level roar through my third-floor window.

In the last two or three weeks I became aware of another sound: a group of men singing or chanting in loud, evidently drunken voices. The song they were singing sounded vaguely sportsy and I supposed it was one of those football chants that rise from the stands of soccer games in the UK and Europe. But when I passed by the Gran Vía plaza I never saw any groups of men who were singing.

So I put a question on Reddit, in the Madrid forum or "subreddit." Titling it (in Spanish) "Why are men singing at night in Madrid?" I explained the situation and asked if anyone else heard them. A couple of people answered and said that these probably were, indeed, football chants, and suggested they might be British fans. A day or two later the same person corrected themselves and said they were Scottish. (Another user commented that "Why are men singing at night in Madrid" was a good title for a novel or story.)

Finally, a few nights ago, I was walking through the shopping/retaurant district just south of the Gran Vía plaza when I saw police lights. I came upon a street where the cops were standing around to monitor a ruckus coming from this side street. Here it was, the source of the singing. I didn't enter the side street, but I saw a crowd of about 200 people standing in the middle of this street in a sort of scrum, a circle with their arms over each others' shoulders. And the participants were wailing some song at the tops of their voices. I wouldn't go so far as to say the song was tuneless, but at the same time it was hard for me to discern the tune. Nevertheless they all knew it and joined in enthusiastically.

I never got close enough to discern their nationality. I couldn't make out the words or even confirm that the words were in English or some other non-Spanish language. Do Scottish football fans sing in Gaelic?

I didn't take a picture; it was growing dark and I figured it would be really difficult to get a good picture of a mass of men from 75 feet away.