[chris (OP)]

In boxers and people who play a lot of rugby, cauliflower ears are common. What causes this phenomenon?

[Chemistry4me]

If the external portion of the ear suffers a blow, a blood clot or other fluid may collect under the perichondrium. This separates the cartilage from the overlying perichondrium that is its source of nutrients, causing the cartilage to die. This leads to a formation of fibrous tissue in the overlying skin. When this happens, the outer ear becomes permanently swollen and deformed, resembling a cauliflower.

http://en.wikipedia.org/wiki/Cauliflower_ear