**Core Concept**
The underlying principle being tested is the understanding of **ankle anatomy** and common injury patterns associated with **Pott's fracture**, also known as a bimalleolar fracture. This type of fracture involves the **distal fibula** and **medial malleolus**.

**Why the Correct Answer is Right**
A Pott's fracture typically results from a severe **ankle inversion** injury, which stresses the **deltoid ligament**. However, the most commonly injured ligament in this context is actually the **anterior talofibular ligament (ATFL)**, due to the mechanism of injury involving forced inversion. The ATFL is the first ligament to be stretched or torn in an inversion injury.

**Why Each Wrong Option is Incorrect**
**Option A:** This choice might be incorrect because, while the deltoid ligament can be injured, it is more commonly associated with **eversion** injuries or severe **pronation**-external rotation injuries.
**Option C:** This choice might be incorrect because, although the **calcaneofibular ligament** can be injured in ankle injuries, it is not the most likely ligament to be injured in the context of a Pott's fracture due to inversion.
**Option D:** This choice might be incorrect because the **posterior talofibular ligament** is less commonly injured compared to the ATFL in the typical inversion mechanism leading to a Pott's fracture.

**Clinical Pearl / High-Yield Fact**
In ankle injuries, especially those involving inversion, it's crucial to remember that the **ATFL** is the most commonly injured ligament, and its injury can be a precursor to chronic **ankle instability** if not properly managed.

**Correct Answer:** D. Anterior talofibular ligament.