How do I judge a backstroke turn?

Under World Aquatics rules (Part Two, Article 6.4), at a backstroke turn:

• The swimmer must touch the wall with some part of the body.
• During the turn the shoulders may rotate past vertical onto the breast. After that, the swimmer may use one immediate, continuous single-arm pull or one immediate, continuous simultaneous double-arm pull to start the turn.
• The swimmer must be back on the back on leaving the wall.

So the breaches to look for are: a pull after turning onto the breast that isn't immediate and continuous, or more than the one pull allowed; no touch on the wall; and leaving the wall not on the back.

At the finish, the swimmer must touch the wall while on the back, and may be fully submerged once the head passes the 5 m mark. Judges of Stroke make sure the backstroke flags are 5 m from each end wall before backstroke and medley events.