Overlap
Being out of order at the moment the server contacts the ball. Each front-row player has to be closer to the net than the back-row player lined up with them. Players in the same row have to keep their left-to-right order. The referee checks this only at serve contact. After that, you can move anywhere.
Example
The setter, playing in the back row, creeps forward until she is even with the front-row player she is supposed to be behind. The server contacts the ball, and the referee whistles an overlap. The other team gets the point.
Frequently Asked Questions
How do you avoid overlapping in volleyball?
Know who should be in front of you and who should be beside you before the server starts. If you are in the back row, stay a little farther from the net than the front-row player you line up with. You can release as soon as the server contacts the ball.
When are overlaps checked in volleyball?
Only when the server contacts the ball. A hitter can run to the pin the instant after contact. A step early is the fault.