I want to know the answer to the following question:
Why did the attack by the Rus go so well on the coast at the start?
All the background I'm provided with is that "At last a Byzantine army arrived from the Balkans to drive the Rus' back, and a naval contingent reportedly destroyed much of the Rus' fleet on its return voyage (possibly an exaggeration since the Rus' soon mounted another attack).". Is that enough to answer the question?