Millwall vs. West Ham rivalry reasons. Are matches dangerous?

Why is there such a rivalry between Millwall and West Ham?
What are the rivalry reasons?
Are matches like this dangerous?

The rivalry between Millwall and West Ham is one the biggest and longest standing in world football. Matches between Millwall and West Ham are known as "Dockers Derby".

The main reasons of Millwall and West Ham rivalry:

• The clubs were founded by workers from competing companies, located close to each other in London docklands.
• Large hooligan firms, Intense hooliganism, Many incidents and fights.

Dockers Derby but also other football derbies are characterized by increased security measures.

I would not call matches like this dangerous, but there is a bit higher risk that some unusual situations may happen.