Concept:
A learning curve represents the progress made in acquiring a new skill over time. In the initial stages of learning, improvement is usually rapid because the learner is highly interested, motivated, and curious about the new activity.
This rapid progress is shown by an increasing gain pattern in the learning curve.
Step 1: Examine Assertion (A).
The assertion states that when an athlete starts learning a new skill, the learning curve shows increasing gain.
This statement is correct because beginners often improve quickly during the early phase of practice.
Step 2: Examine Reason (R).
The reason explains that the initial rapid rise occurs due to novelty, curiosity, and interest in the new activity.
This statement is also correct.
Step 3: Determine whether the reason explains the assertion.
The reason correctly explains why the learning curve initially rises rapidly.
Hence:
\[
\boxed{\text{Both (A) and (R) are correct and (R) is the correct explanation of (A)}}
\]
Therefore, the correct answer is:
\[
\boxed{(A)}
\]