RedactedNarrative: Vessel #1 was drifting while the vessel was idling in neutral.  Operator #1 stood up without shutting down the engine to adjust his shorts and life jacket when he lost his balance and his right leg hit the throttle causing the vessel motor to be engaged in reverse.  
  Occupant #3, who was sitting on the swim platform at the same time the vessel entered reverse gear, entered the water and his life jacket was immediately entangled with the vessel's prop, which contributed to his injuries.  Occupant #4 was also knee-boarding that day and in the water during this incident.  Operator #1 entered the water and was able to free occupant #3 after realizing what happened.