Defendant Siale Angilau was hospitalized with at least one chest wound, FBI spokesman Mark Dressen said. The witness wasn't hurt.
Angilau was one of 17 people named in a 29-count racketeering indictment filed in 2008 accusing gang members of conspiracy, assault, robbery and weapons offenses.
Angilau was the last defendant in the case to stand trial, US attorney's office spokeswoman Melodie Rydalch said. Angilau's attorneys, Michael Langford and Mark Kittrell, did not immediately respond to messages.
The case was being heard in US District Judge Tena Campbell's courtroom.
