Final answer:
The key difference between an early sidearm striker and a proficient sidearm striker is that the proficient sidearm striker uses a more direct arm swing and has more hip rotation, leading to a more powerful and accurate pitch.
Step-by-step explanation:
The key difference between an early sidearm striker and a proficient sidearm striker is related to their throwing mechanics in softball. Specifically, the difference lies in the arm swing and hip rotation during the pitch. Option (B) states that a proficient sidearm striker uses a more direct arm swing, which means the arm path is more efficient and streamlined toward the target, leading to a potentially faster and more accurate pitch. Option (D) suggests that a proficient sidearm striker has more hip rotation, which is an important aspect of an effective pitching motion. Proper hip rotation contributes to the generation of significant power and speed in the pitch, evident by the fast pitch speed mentioned in the reference question.