Leadership can take place in the smallest of instances. Say, card games are supposed to be over at a certain time, or the TVs are supposed to be turned off at a certain time. Players are wont to push the rules. We all do that. Leaders on a ball club will walk by and say, 'Rules are rules.
Players police themselves that way.
On any good ball club, players police themselves on and off the field very, very well. Say someone makes a small mental mistake, like overthrowing the cutoff man. A coach or the manager will say something. Or a rookie will strike out with two out and the bases loaded, or make a game-ending error to lose the game. A veteran player will take him aside and not necessarily console him, but help him understand that to be successful in this game you've got to learn how to deal with failure.