presumptively prejudicial

In a criminal case, any private communication, contact, or tampering directly or indirectly, with a juror during a trial about the matter pending before the jury is, for obvious reasons, deemed presumptively prejudicial, if not made in pursuance of known rules of the court and the instructions and directions of the court made during the trial, with full knowledge of the parties. The presumption is not conclusive, but the burden rests heavily upon the Government to establish, after notice to and hearing of the defendant, that such contact with the juror was harmless to the defendant.

Defined by the Supreme Court in - Remmer v. United States, 347 U.S. 227 (1954).

See also 350 U.S. 377.