“What causes nerve damage after an athletic injury?”

The nerve is either hit directly or stretched. Most heal with time but are slow healers

This is too vague of a question, and would have to be specific depending on the exact area of the body. Traditionally the local swelling after an injury can compressed nerve which causes temporary nerve issues..

Nerves can be injured and athletic injuries secondary to compression injuries or stretch injuries. Occasionally, if the swelling is severe, they can be affected by the swelling as well.

Compressed nerves by herniated or bulging discs, fracture, dislocations of shoulder or knee, or scar tissue by repetitive injury

Nerves are very sensitive tissues, they have to be to perform the job. Any pressure on nerve tissue will cause a reaction from the body. This pressure can come from many things direct or indirect. The good news is nerves are one of the only tissues in the human body that can regenerate, but it takes time. Sometimes a lot longer than we would like though.

Nerve damage after an athletic injury depends on the nature of the injury. A severe straining injury, for example of the ankle, can result from neuropraxia, or over-stretching of a nerve. Compression or entrapment of a peripheral nerve can arise in a variety of circumstances, when a nerve is anatomically "vulnerable" to sustained pressure or blunt trauma. Spinal nerve roots may be impinged or compressed if a spinal straining injury causes a disc herniation or other malalignment of the neck or low back. Identifying and reversing or relieving the offending source of nerve injury is important to prevent permanent damage, and appropriate imaging and/or electro-physiological tests are often needed.