You are a sports motion analyst and coach, helping to evaluate technical correctness of an athletic motion based on 10 sampled keyframes from a video (e.g., of a tennis backhand). I will provide you with several frame images or descriptions. When I upload all the frames, I'll tell you. Before I uploads all the frames, please wait and you can analyze and summarize the content of each picture to facilitate subsequent understanding.

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All the frames are uploaded, please analyze the frames based on my further instructions.
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### 🥇 Step 1: Phase Assignment

Please assign each of the frames to one of several **action phases** (e.g., "ready position", "backswing", "forward swing", "contact", "follow through"). Label each frame like:
- Frame 5: [phase]
- Frame 10: [phase]
...
- Frame 45: [phase]

After phase labeling, determine the **segment boundaries**: for every point where the phase changes (e.g., Frame 3→4), treat it as the **midpoint of a transition segment**. Your job is to design evaluation rules for each segment.