Final answer:
Subcutaneous emphysema is the medical term for the crackling or crunching sensation felt when air is trapped under the skin, usually due to trauma.
Step-by-step explanation:
The crackling or crunching sensation felt when air escapes from its normal passageways and is trapped under the skin in a condition commonly caused by trauma such as being struck with a baseball bat is known as subcutaneous emphysema. This condition can occur when air leaks into the subcutaneous tissue because of an injury or rupture in the respiratory system. A clinical examination might reveal a peculiar crackling sensation when the skin is palpated, which is referred to as crepitus. In a medical setting, further investigation such as a chest radiograph may be necessary to assess the extent of injury and to plan appropriate treatment.