Multiple referees have been sent home from the NCAA men’s basketball tournament’s controlled environment in Indianapolis due to a positive COVID-19 test and contact tracing, the NCAA said in a statement Monday night.

Per the NCAA, one official tested positive on Monday and had interacted with five other officials. All six were sent home. Four of the refs have been replaced from a pool of reserves; two won’t be replaced.

“The NCAA has replaced several officials for March Madness because of a positive COVID-19 test,” the NCAA said in a statement. “One official tested positive March 15, and five other officials the person interacted with the day before were identified as exposure risks due to prolonged close contact. Based on tournament protocols and contract tracing with local public health authorities, these officials may not participate in the tournament. The infected official must be placed in isolation, and the other officials must be placed in quarantine.”