Question

if you watch a professional baseball game attentively, you will see a subtle game within the game: a sequence of wordless signals passing among members of a team. these seemingly arbitrary gestures—a player scratching his nose and then tapping his right forearm, a coach tugging his cap three times in succession—are actually a secret, closely guarded code to communicate strategy within the team. an adjustment of a cap might be an instruction for a batter to bunt the ball; a hand in the back pocket could indicate that a player should steal a base. as you might expect, opposing teams expend enormous effort to crack each others codes. for this reason, teams not only change their codes often but also intersperse meaningless decoy signals with the real ones, just to confuse the opposing team.
what is the main, or central, idea of the passage?

Explanation:

The passage focuses on the subtle wordless signals in professional baseball, explaining they are secret strategy codes and noting teams' efforts to protect these codes from opponents.

Answer:

Professional baseball teams use secret, wordless signal codes to communicate strategies, and they take measures like changing codes and adding decoy signals to prevent opposing teams from cracking them.