This lesson matters because angle conventions for motion interpretation sits at the point where raw tracking data becomes baseball action. A staff can collect thousands of points, but if the geometric interpretation is loose, recommendations become noise dressed up as certainty. In this topic, the recurring operational pain is disagreement over launch and approach angle signs across tracking tools. When that pain is unresolved, players receive mixed cues, analysts lose credibility, and postgame review becomes an argument over notation instead of baseball development. The fix is disciplined geometric modeling: define objects, define assumptions, compute with the right relationship, and report the result in language that survives cross-department handoff. We treat geometry as a decision system rather than a worksheet. Every quantity must connect to a practical choice: where to stand, when to move, what route to prefer, and what uncertainty should limit confidence. By the end of the lesson, students should be able to justify not only the number they computed, but also why that number is the right number for the decision context in front of them.