Which of the following is NOT a type of entrapment?

The correct choice highlights that "ball entrapment" is not recognized as a type of entrapment related to pool safety. In the context of pool operations, entrapment refers to situations where a swimmer can become trapped against a drain or suction outlet, which poses serious safety risks.

Hair entrapment, for instance, occurs when long hair gets caught in the suction of a drain, leading to a dangerous situation. Body suction entrapment involves a person's body being held against a drain due to the strong suction, which can cause significant harm. Mechanical entrapment generally refers to situations where an object or a swimmer can become trapped due to pool fixtures or equipment.

In contrast, "ball entrapment" does not represent a recognized category of entrapment in pool safety literature and does not describe a specific hazard associated with pool drains or suction outlets. Thus, it accurately identifies the option that does not fit within the established types of entrapment.