how did the population of black attending the trial react to atticus?

The black people stand out of respect for Atticus. They understand the sacrifices Atticus made to take this case. They understand the passion and commitment Atticus had for a cause that was defeated even before he started. Despite Tom Robinson losing his case, the Black people on the second level all stand up as Atticus leaves. Rev. Sykes turns to Scout and says, "Jean Louise, stand up. Your father's passing."