Breakdown of Когда начался дождь, люди разбежались.
дождь
rain
люди
people
когда
when
начаться
to start (perfective)
Questions & Answers about Когда начался дождь, люди разбежались.
How does the combination of раз- and -ся change the verb in разбежались?
The prefix раз- combined with the reflexive particle -ся on a verb of motion adds the meaning of 'scattering' or 'moving apart'. It turns the base verb бежать (to run) into 'to run away in different directions'.
Could I just say люди убежали instead?
You could, but it changes the scene slightly. Убежали simply means they 'ran away' or 'departed'—they could have all run together to the exact same bus stop. Разбежались specifically emphasizes that the crowd broke up and scattered in multiple different directions.
Why do verbs of motion with the раз- ... -ся pattern usually take a plural subject, like люди here?
Because the core meaning is 'scattering' or 'moving apart', you need multiple entities to move away from each other. You cannot logically 'scatter' if you are just one person, so you will almost always see these verbs used with plural subjects.
Why is the prefix spelled раз- here rather than рас-?