What is the antenna rule in volleyball?

The ball must cross the net entirely between the two antennas (and their imaginary extensions). A ball that contacts the antenna or passes outside it is out of bounds and the opponent scores.

Full Explanation

Per FIVB Rule 2.3, the antenna is an 1.8-meter flexible rod attached to the outer edge of each sideline band of the net. The antennas mark the lateral boundaries of the crossing space. Per FIVB Rule 10.1.2, the ball is out if it contacts an antenna or passes beyond the antenna to the opponent's court. If a player hits the antenna while attacking or serving, it is a fault. Line judges are responsible for signaling antenna touches. The same rule applies under USAV, NFHS, and NCAA rules.

Rulesets covered: FIVB/USAV/NFHS/NCAA  |  Rule Reference: FIVB Rule 2.3; FIVB Rule 10.1.2