A crowd is a large group of people who have gathered together, for example
to watch or listen to something interesting, or to protest about something.
A huge crowd gathered in a square outside the Kremlin walls...
The crowd were enormously enthusiastic...
The explosions took place in shopping centres as crowds of people were shopping for Mothers' Day.
If a situation or problem arises, it begins to exist or people start to become aware of it.
The birds also attack crops when the opportunity arises. = occur
If something arises from a particular situation, or arises out of it, it is created or caused by the situation.
...an overwhelming sense of guilt arising from my actions.
When you arise, you get out of bed in the morning. (FORMAL)
He arose at 6:30 a.m. as usual.