In this "clicker case study," students learn about the chemical nature of protein molecules-in particular, how the constituent parts of proteins (amino acids) contribute to protein three-dimensional structure and folding. Several important human diseases, such as cystic fibrosis, BSE (Mad Cow disease), an inherited form of emphysema, Alzheimer's, and even many cancers are believed to result from protein miss-folding. Students often view these as "old-people" diseases, but may be unaware that many athletes suffer from dementia and have problems much like Alzheimer's at a very early age due to concussions suffered in their sport, a condition called Chronic Traumatic Encephalopathy (CTE). This case focuses on the efforts made by fans and ex-players to highlight the serious problem of head trauma and the resulting CTE symptoms caused by protein-filled plaques seen in many pro-football players, boxers, and even wrestlers. As students learn about what causes CTE, they begin to see the need to understand protein composition and folding, and how amino-acid composition and folding affect protein function.