An assault victim presents with a rigid and tender abdomen alongside vital signs of BP 110/70, P 118, and R 26. What is the most likely diagnosis?

In this scenario involving an assault victim with a rigid and tender abdomen, elevated pulse (tachycardia), and increased respiratory rate (tachypnea), the most likely diagnosis is abdominal trauma.

The presentation of a rigid and tender abdomen is highly indicative of a significant abdominal injury, which may occur as a result of blunt force trauma, such as an assault. This rigidity, often referred to as "guarding," can suggest peritoneal irritation or bleeding within the abdominal cavity. The vital signs indicating a slightly low blood pressure and increased heart rate further support the potential for internal injury or bleeding, as the body may be responding to hypotension with compensatory mechanisms.

While a ruptured diaphragm could present with some similar symptoms, it is typically associated with specific respiratory distress and may present with atypical signs that are not articulated in this scenario. Appendicitis generally causes localized pain in the lower right quadrant with a progression of symptoms that may not match the rigidity observed here, and while internal bleeding could also lead to a rigid abdomen, in this context, it is specifically the trauma that is most consistent with the assault.

Thus, abdominal trauma is the most coherent diagnosis given the provided signs and circumstances surrounding the case.