Fig 2. Bottom turn (BT) and cutback (CB) maneuvers.

A) Surfer drops into a wave at t = 0, with speed 9.2 m/s. B) Bottom turn maneuver at t = 0.79 s with speed = 11.5 m/s. Note speed gain compared to A), and how surfer has rolled board onto the “back side.” C) Transition to cutback at 1.25 s, with speed 10.1 m/s. Speed drops (compared to C) as surfer pitches board and climbs wave face. D) Cutback maneuver, or top turn at t = 2.21 s. Note large amount of spray generated, and how board is now rolled onto the “front side.” The transition from back side to front side delineates the bottom turn from the cutback maneuver. See also Fig 4 and S1 Video for more details of the turn represented in A-D). E) Schematic representation of surfer’s trajectory depicted in A-D).