Most were young lads in their 20s, coming down the hill in wave after wave. But not all.
There were women and older men too. One, probably in his late 50s or early 60s, wore a green and gold scarf and woolly hat - the colours of United's first shirts when they were formed as Newton Heath in 1878, and of the original anti-Glazer protests in 2010
After he had left the stadium compound, he remained with those waiting for the United team bus that never arrived.
He was not angry and spoke calmly to fans and media in the same area, wanting to know the latest about what was happening on the other side of the ground, or around the team hotel, where he had been earlier.
Those fans, he felt, were more sinister than the ones at the stadium. But he didn't condemn them. He accepts they have a common goal. Emotions have been simmering for 16 years, so a bit of aggression is understandable, the theory went.
Exchanges like this - and people like that - underline the reason for what happened at Old Trafford.
A large protest was expected outside the ground before the match with historic rivals Liverpool - but no-one expected fans to force their way into the stadium and on to the pitch and for the match to be postponed.