Different sports have different penalties for infractions and egregious fouls, to which soccer has its own special and unique rules dealing with these incidents. In soccer, there are two basic offenses, there is the straight red card which is issued to players for the most serious fouls and for obvious infractions such as illegally denying the opposing team a goal-scoring opportunity, and then there is the yellow card, for bad fouls that aren't quite worthy of the red card, persistent fouling, professional fouls, and other assorted things that are an infringement to basic good sportsmanship. The difference between a red card and a yellow card, is a red card is an immediate dismissal from the game itself, whereupon, that team will have to play the remainder of the match shorthanded, which is a significant disadvantage, whereas for the first yellow card on a player, there is no dismissal, however, for a second yellow card on the same player in the same game, those two yellow cards equate to a red card, and the player is dismissed from the field of action. So in summary, a red card means immediate dismissal from the game, whereas one yellow card is a caution to a particular player, but should that player get a second yellow card they too will be dismissed from the game. In soccer, it is neither infrequent for a red card to be issued to an offending player, nor is it infrequent for one player to be dismissed through two yellow cards. However, in regards to a yellow card, the field manager of the team does have an option, of removing said player from the field through a substitution if he has not already used up all his substitutes. Anytime, any player receives a yellow card on the field, a good manager should immediately consider his options so as to better protect his team from suffering the ill effects of a second yellow card, and consequent dismissal of that player.
As discussed in the newyorker.com, it is estimated that the removal of a player from the soccer field, "… cost the offending teams about .015 goals per minute left in a game," which basically means that playing short-handed is not something that you ever want to have occur to your team. This should signify, that when any player receives a yellow card, the manager should determine that player's value as compared to the disadvantage of being short-handed, should that occur, and consequently that is why a manager should make it a liberal policy to substitute players that are on a yellow card. Of course, not all players are created equal in either their abilities or in their propensity to get a second yellow card. For instance, neither goal keepers nor strikers should typically need to be replaced, because strikers typically have limited defensive duties, whereas goalkeepers are typically given the benefit of the doubt in controlling their area of the pitch. However, for defenders, to which it is their main purpose to prevent the opposing side from getting good chances on goal, as well as midfielders that are there to control the pace and content of the game, serious consideration for their removal must be taken into account. The fact of the matter is there are only possibly a few elite players in the game that are worth .015 goals per minute, so the better part of valor is to err on caution and subsequently to take the issue of a yellow card to your player as something that does necessitate a valid counter-move.