Ever wondered why wrestlers around the world have weird ears?

Blunt trauma or other injury to the ear, such as what may occur during a boxing or wrestling match, might result in deformity of the ear pinna, which is often referred to as the "boxer's ear" or "cauliflower ear".

How is it caused?

Most common cause is hit(s) to the ear that leads to stripping of the perichondrium from cartilage of ear pinna, and this in turn result into hematomas (i.e. small collections of blood that clot and block the flow of blood and nutrients). When blood flow is blocked, the affected cartilage may die and, without the supportive tissue, fold in on itself. Scar tissue may form, contributing to a swollen bumpy or lumpy appearance on part of the ear, similar to a cauliflower.
Usually, cauliflower ear is related to sports injuries (hence, called "boxer's ears"), but not always. Any trauma to the ear can cause it. Cauliflower ear can even be the result of an infection in the ear lobe.

Depiction of cauliflower ear in the Boxer of Quirinal, circa 100–50 BC

Treatment

The goal of treatment is to ease the blockage so that blood can again flow to the affected tissues. A doctor can accomplish this by making a small incision and draining accumulating blood or removing a clot and preventing further bleeding. They may need to reconnect tissues using stitches and apply a special bandage to put pressure on the area.

Prevention

Early treatment can help prevent permanent deformity.
The most important thing you can do to prevent cauliflower ear is to wear the appropriate head gear when engaging in activities that increase your risk for ear trauma, such as wrestling, boxing, rugby, and other close-contact sports. 
Also, ear piercings are not recommended on the cartilaginous part.

Now, that you are aware of the risks, you must visit a doctor to evaluate any trauma to the ear, even if it seems superficial. Early treatment can help prevent permanent deformity.