On the course side is an expression used in sailboat racing to indicate that a boat was on the wrong side of the starting line when the starting signal was given. According to the Sailing Instructions valid for a specific racing event, being on the course side may entail an immediate disqualification, or it may allow to maneuver for correcting the start procedure.
The corresponding scoring abbreviation is OCS,[1] whose technical meaning is as follows:[2]
OCS Did not start; on the course side of the starting line at her starting signal and failed to start, or broke rule 30.1
— 2017-2020 Racing Rules of Sailing, p. 57, World Sailing (Southampton, UK, June 2016)