Domain: Humanities and Social Sciences — Sport
Target concept: Dolphin kick: The dolphin kick consists of a hip-initiated undulation that bends the knees and travels down through the ankles, with the legs and feet kept together throughout, pushing water backward. It is labeled as dolphin kick. During the kick, the feet stay joined (not turned outward), with a fixed rhythm and unique movement sequence.

Video generation prompt: Demonstrate the prone position of a swimmer, and perform the dolphin kick movements in the pool. The movements should be slow, clear, rhythmic, and repeated once.

Evaluation guide:
(i) Target concept: A single-cycle, biomechanically accurate dolphin kick executed from a stable prone position in water.
Minimum mechanism: Water must behave as a Newtonian fluid medium that visibly deforms in response to directional limb force; the kick is driven by a hip-initiated undulation that travels through the knees to the ankles, with the legs and feet kept together (not splayed apart) throughout; the recovery (upbeat) involves knee flexion with the heels rising toward the surface, and the propulsive phase (downbeat) involves the legs extending downward-backward together, generating rearward momentum transfer visible as water displacement behind the feet.
(ii)Storyline: [Frame 0] Swimmer fully immersed, motionless, prone, horizontal, legs together, centered in pool view. → [Early phase] Hips dip first, initiating a wave that bends the knees while the heels rise toward the surface; the feet stay together throughout. → [Mid-phase] Knees reach peak flexion with the ankles relaxed and pointed, legs still joined. → [Late phase] Legs snap downward and backward as a single connected unit, ankles trailing last, driving water rearward. → [Final frame] Motion completes; water displacement persists visibly behind the feet; swimmer remains prone and stationary, no follow-through motion. Perspective: Fixed side/frontal view ensuring full visibility of torso alignment, knee angle, leg-together posture, and water reaction; no occlusion of critical joints or water interface.

Manual:
Experimental Procedure
1. Swimmer enters pool and assumes stable prone position (face down, arms extended forward or at sides, body horizontal, legs joined together).
2. Perform one complete, slow, rhythmic dolphin kick: hips initiate the undulation → knees bend as heels rise (recovery) → legs extend downward and backward together as one unit (propulsion), feet remaining joined throughout.
3. Maintain prone position throughout; no arm movement or breathing motion.
Observation of Experimental Phenomena
- Swimmer remains fully prone with no vertical lift or rotation.
- The undulation visibly originates at the hips and travels down through the knees to the ankles.
- Feet and legs stay together (not splayed outward) through the entire cycle.
- Legs move as a single connected unit downward and backward during the propulsive phase.
- Clear backward water displacement originates from the feet during the downbeat.
Summary of Experimental Principles
Dolphin kick propulsion comes from a hip-driven undulating wave that passes through the knees to the ankles, with the legs kept together throughout; the resulting whip-like downward-backward leg extension pushes water backward, generating forward thrust.

Prompt Grounding rubric:
level_1: No swimmer present in the pool; or the swimmer is not in a prone (face-down, horizontal) position; or no leg movement is visible; or the kick is not repeated exactly once (e.g., zero times or several cycles run together); or the motion is too fast, blurred, or jerky to follow; or the setting is not a swimming pool.
level_2: Swimmer is present, prone, and in a pool, but the leg action shown is not a dolphin kick: e.g., the legs alternate out of phase (flutter kick) or splay apart during the power phase (breaststroke-style whip kick), or the legs are absent from view; or the kick repeats more than once or not at all; or the tempo is irregular (uneven pauses or sudden speed changes) rather than steady and rhythmic.
level_3: Swimmer is prone in the pool; the legs move together (not splayed apart) through one full slow, clear cycle in the water; however, the hip-to-ankle undulation is not visible, OR the knee bend during recovery is not clear, OR the backward water displacement behind the feet is not discernible.
level_4: Swimmer is prone in the pool; the legs stay joined throughout one slow, clear, rhythmic cycle; knee flexion during recovery and a downward-backward leg extension during propulsion are both visible; water displacement appears behind the feet; all prompt elements are present except one non-core flaw (e.g., slight torso lift, minor head tilt, or brief occlusion of the feet by splash).
level_5: Swimmer is prone in the pool; the legs remain joined throughout one slow, clear, rhythmic cycle that unambiguously reads as a dolphin kick: hips dip → knees bend as heels rise → legs extend downward-backward together as a single unit → visible backward water displacement behind the feet; no occlusion, no posture deviation, no repetition error, no timing ambiguity, no environment mismatch.

Scientific and Causal Correctness rubric:
level_1: Movement contradicts dolphin-kick biomechanics: e.g., the legs move independently of each other (alternating/flutter pattern); the knees stay locked straight throughout; the feet splay apart during the power phase; no backward water displacement is visible; or the action resembles a breaststroke whip kick or freestyle flutter kick instead.
level_2: Knees bend during recovery but the legs separate rather than staying joined; OR the legs stay joined but the extension is directed forward or upward instead of downward-backward; OR no water displacement is visible behind the feet; OR the undulation appears to originate at the knees or ankles rather than being initiated at the hips.
level_3: Hips initiate the undulation and the knees bend with the legs kept together during recovery; the legs extend downward-backward as a joined unit during propulsion; water displaces visibly behind the feet; however, the rhythm is inconsistent within the single cycle (e.g., a pause mid-kick or an abrupt speed change), OR the causal link between leg extension and water displacement is ambiguous (e.g., displacement appears before the legs finish extending).
level_4: All phases are visually correct and causally ordered: hip-initiated undulation precedes knee flexion; knee flexion with legs together precedes the downward-backward extension; the extension coincides with visible backward water displacement; the rhythm is internally consistent within the single cycle; only one non-core deviation is present (e.g., a minor surface-ripple mismatch or a brief loss of body streamlining).
level_5: Every phase of the dolphin kick appears in the correct causal sequence: (1) hips initiate the undulating wave, (2) knees bend as the legs stay joined during recovery, (3) legs extend downward and backward together as a single unit, (4) water displaces visibly backward from the feet, with no phase skipped or reversed, no leg separation at any point, and no ambiguity in the action-to-water-reaction relationship.

Spatiotemporal Consistency rubric:
level_1: The swimmer's position or a limb jumps to a different location between consecutive frames; a leg or foot vanishes and reappears; the water surface breaks apart or reforms instantaneously; the framing or zoom level changes abruptly mid-kick; the background scene changes; a limb detaches or visibly distorts in shape; or the overall scene brightness switches abruptly between bright and dark with no visible cause.
level_2: A noticeable but less severe break occurs: e.g., the swimmer's head position shifts inconsistently relative to the pool edge between frames; the water surface level changes unnaturally between frames; the legs appear to double or strobe during motion; the direction of the shadow beneath the swimmer changes partway through the cycle with no corresponding change in the light source; or background elements flicker in and out.
level_3: The swimmer stays fully visible and holds the prone position throughout; the legs stay visibly attached and continuous in shape; the water surface deforms gradually rather than in sudden jumps; the shadow beneath the swimmer keeps a consistent direction and strength across the sequence; the camera view stays fixed at a side or frontal angle that keeps the torso and legs in frame, except for one minor break, such as a 1-2 frame occlusion of the feet by splash or a brief motion blur that still leaves the joint angles readable.
level_4: All conditions for the score 3 are met, AND the framing never pans, tilts, or zooms, AND the water deformation builds and recedes continuously from the knee-bend to the leg-extension phase with no sudden jumps, AND every body segment (thigh, shin, foot) stays visibly connected and proportioned the same size throughout; only one small, non-core spatiotemporal flaw remains, such as a faint edge artifact at the pool rim or an inconsequential wobble in a background tile pattern.
level_5: No spatiotemporal artifacts are visible: the swimmer's body stays continuously present, proportioned, and connected across every frame; the leg motion flows without any interruption, warping, or decoupling of segments; the water displacement rises and settles smoothly in step with the leg motion; the shadow beneath the swimmer stays consistent in direction and strength across the whole sequence; the camera view stays fixed and keeps the prone torso and full leg trajectory in frame throughout.