“Swaying while balancing” is one of four “clues” used by a police officer to detect intoxication during the One-Leg-Stand component of the Standardized Field Sobriety Test (SFST). The police officer would require only one other clue to mark the suspect down as having failed this component and arrive at the conclusion that there is a 65% (according to the latest SFST training manual) or 83% (based on NHTSA’s latest estimates) chance that the suspect’s blood alcohol content is over the legal limit.
The suspect is also required to remain perfectly still with his feet together and his hands heads at his side during administration of the horizontal gaze nystagmus (HGN) test. Any swaying by the suspect would compromise the validity of the results from the HGN.
In what Taylor/Oberman have termed the “disappearing sway” phenomenon, it is amazing how many suspects fail the “swaying while balancing” clue while remaining perfectly balanced and still during the HGN test.