August Wilson's plays are almost always pretty "realistic." They have to do with everyday people in pretty everyday situations. Almost all of Wilson's characters are black and they speak in an African-American dialect which is pretty similar to the one spoken in Wilson's native Pittsburgh.
Of course, Wilson's plays also have an incredibly poetic quality to them. His characters have the ability to speak in ways that are far more heightened than what you typically find in everyday speech. For this reason, we say the play is not just realism, but poetic realism. Many great American playwrights often wrote in a similar style, including Tennessee Williams, Arthur Miller, and Eugene O'Neill.