When I was in high school, the coach had us run wind-sprints at the end of practice. We were tired from all the drills and scrimmaging.  You could always see who had practiced, because their uniforms were embedded with dirt, sweat and, at times, blood. These were the ones who participated in scrimmages. Basically, those that played in the game. After about ten 40-yard wind-sprints, the coach would call-out, “Who has something left?” One player responded, “I got something left; I can run more wind-sprints.” The coach then went ballistic running over to the player who responded, yelling at him why he held something back in practice. “Why do you have anything left? You should have given me your ‘all’ running the plays and drills.” We all had to run more wind-sprints to make sure we did not leave anything on the field. No one ever boasted again that they had anything left.