Your goal is to earn a million dollars as a professional athlete, and you get to become best in the world at one specific athletic skill.

Your goal is to earn 10 million dollars in professional sports. You get to choose one specific skill to become the best in the world at. Everything else about you and your skill set would stay the same.

For the sake of argument, you are the correct age to be a professional athlete (i.e. ~25 years old), but otherwise complete unknown with no established athletic history, so you’d have to work your way up from obscurity.

Some examples:

For baseball you could choose throwing a fastball, but don’t know how to throw any other pitches. Or you could become a world class hitter but your running speed and throwing skills are what they currently are.

For tennis, choose forehand, backhand, volleys, or serve.

For golf, you get a single shot. Drive, pitch, putt, etc.

For basketball, you could choose to have the best jump shot in the world, but your athletic skills are otherwise the same.