Castiglione joined the Red Sox broadcast team in , teamed with Ken Coleman. He admitted not being in the booth when the ball rolled through Bill Buckner's legs in the 1986 World Series, as he was in the clubhouse covering Red Sox' seemingly impending victory celebration. After Coleman's retirement in 1989, Bob Starr became the lead announcer for the Red Sox. After Starr's departure at the end of the 1991 season, Castiglione became the team's lead radio announcer along with Jerry Trupiano. Castiglione became nationally known when the team won the 2004 World Series, with his broadcast of the end of the game. His jubilant "Can you believe it?" after the final out became a catchphrase.