system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Why, especially in sports, do people put their hands on their heads when disappointed or upset?
gpt
When training you are often taught to place your hands on your head to help recover and catch your breath after vigorous activity. It promotes stretching of the chest allowing full inflation of the lungs to speed up recovery. 

Combine this with a player experiencing disappointment and you have someone suddenly noticing their tiredness in a combination of exasperation and fatigue.