The voice-over refers to several bombings carried out by Ayers' organization, the Weather Underground. One of those was a judge's house. The story of that incident, as told by the judge's son is here. After first trying to minimize his relationship with William Ayers as "some guy who lives in my neighborhood," Obama is now trying to justify it on the basis that he was only 8 years old when Ayers and his terrorist group were carrying out their attacks. John Murtagh, the judges son, was only 9 when the Weathermen tried to murder his entire family.
The issue with the Obama/Ayers relationship isn't, as some are trying to paint it, implying guilt by association but the fact that Obama is hanging out with someone who is proud of his terrorist acts, has never paid any meaningful price for them and has stated that he wouldn't rule out doing it again. Like it or not, we are all judged by the company we keep and Obama keeps company with some very bad people.