|What's that red/black flag with the three white crosses?|
It's the flag of the city of Amsterdam.
|How do Ajax fans call Feijenoord fans ?|
They call them 'Kakkerlakken' (cockroaches).
|Why do you see Israelian flags at Ajax matches?|
Ajax fans were called 'Joden' (yids/jews) by fans from other teams. The Ajax fans turned things round and started to call themselves 'Joden' too. They express that by using the Star of David as their symbol.
|How do Feijenoord fans call Ajax fans ?|
They call them 'Joden' (Yids) because Ajax has some Jewish history, it isn't a Jewish club though. They are also called 'Neuzen' (Noses) because of the perception that Jewish people have big noses.