Some people are "wired" for greater emotions or possibly tears. It takes extra work to overcome this and as children it needs to be understood that they have less experience and practice with managing emotions than an adult. It is that simple. However, with sports, professional settings, and other environments, crying and excessive emotions are detrimental.
In baseball, my son cares so deeply, is so competitive, expects so much of himself, and hates to let the team down. When he strikes out or has a bad hit that is easily fielded, he often cries. My DH and I DO NOT LIKE THIS AT ALL. But he is 11 and he wired for intense emotions. The problem is his tears can negatively affect HIS performance during the rest of the game and impacts the team's energy and outlook.
We tell him that during competition he needs to be a leader, control the display of emotions (what he feels is ok), and focus energy on positive behaviors. Generally, this goes for practice too, although crying tends not to happen during practice. Crying should be kept for in the car or at home - that simple.