NANTUCKET, Mass.—Actor Kevin Spacey didn’t speak during his appearance Monday in a packed district court here, where his lawyer entered a not guilty plea in response to allegations he sexually assaulted a young man in 2016.

Mr. Spacey, known as Kevin S. Fowler in court documents, wore a gray suit and both sat and stood during the roughly 10-minute hearing. Judge Thomas Barrett ordered Mr. Spacey released under the condition he stays away from the alleged victim and his family.

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