It is not usual to see NFL players crying during or after a game, but there are a few instances. Tears can be a result of emotional or physical pain. Players who shed tears are often very attached to their teammates and fans.
One notable incident is when Knowshon Moreno emotionally responded to the national anthem when Denver Broncos played against Kansas City Chiefs. This happened on December 2, 2013. It showed his deep love for the country.
According to an article by American Psychological Association (APA)'s Monitor on Psychology, NFL players also face an increased risk of mental health issues such as depression and aggression. This disturbs their emotional well-being and could also be a reason for their tears.
Fans, too, may shed tears when their favorite team wins or loses a game.