A penalty in rugby union is the main disciplinary sanction available to the referee to penalise a team who commit deliberate infringements.
The referee signals that he has awarded a penalty to a side by raising his arm at 45 degrees between vertical and horizontal and blowing a blast on his whistle.
Equally, a referee may warn a team about technical infringements (especially at the scrum and ruck) before penalising them.
If a kick is taken, the side that the penalty was awarded against must retreat 10 metres (or to their goal line if closer).
This was dropped after variable application by referees, but remains a rugby union rule.