Select the option that best explains the underlined idiom in the given sentence.
A team's captain always keeps a level head, even in the most challenging situations.

The correct option is Remains calm and composed.

Understanding the Idiom:
An idiom is an expression whose meaning is not predictable from the literal definitions of its individual words. The idiom "keep a level head" means to remain calm, sensible, and composed, especially when dealing with difficult, stressful, or challenging situations.

Contextual Analysis:
In the given sentence, a team captain is described as keeping a level head "even in the most challenging situations." During stressful moments in a game or conflict, a leader must avoid panicking and make rational decisions, which requires staying calm and composed.

Evaluating the Options:
- "Prefers to keep his head covered with a cap": This is an incorrect, literal interpretation of covering one's head.
- "Maintains an equal number of players on the field": This misinterprets "level" as making things equal or balanced on a field, which is unrelated to the idiom.
- "Remains calm and composed": This is the correct meaning of keeping a level head.
- "Keeps his head protected with a helmet": This is another incorrect, literal interpretation concerning physical head protection.