**Core Concept**
The ankle joint is stabilized by multiple ligaments, which can be injured due to various mechanisms of trauma. The most common ligament injured in ankle injuries is the one that provides medial (inner) stability to the joint.

**Why the Correct Answer is Right**
The **Anterior Talofibular Ligament (ATFL)** is the most commonly injured ligament in ankle sprains. This is because the ATFL is the first line of defense against excessive inversion (rolling inward) of the ankle joint, and it is often subjected to excessive stress during ankle inversion injuries. The ATFL connects the anterior (front) aspect of the fibula (outer lower leg bone) to the talus (ankle bone) and plays a crucial role in maintaining the integrity of the ankle joint.

**Why Each Wrong Option is Incorrect**
* **Option A:** The **Calcaneofibular Ligament (CFL)** is also a stabilizing ligament of the ankle joint but is less frequently injured than the ATFL.
* **Option B:** The **Posterior Talofibular Ligament (PTFL)** provides posterior (rear) stability to the ankle joint and is not the most common ligament injured in ankle sprains.
* **Option D:** The **Deltoid Ligament** is a medial stabilizing ligament of the ankle joint but is less commonly injured than the ATFL.

**Clinical Pearl / High-Yield Fact**
Remember the **"ATFL"** rule for ankle sprains: **A**nterior, **T**alus, **F**ibula, and **L**igament. This mnemonic can help you recall that the ATFL is the most commonly injured ligament in ankle sprains.

**Correct Answer: A. Anterior Talofibular Ligament**