Substitutions are limited in soccer throughout the duration of each game. Allowing several replacements in a game may result in an excessive amount of play breaks. You may have witnessed this firsthand. There is no restriction on the number of replacements that can be made in some non-competitive or "friendly" soccer games. The substitution rule is one of the most complicated in sports. It is explained in detail below, but essentially, you are only allowed a certain number of substitutions per game. If you use more, the other team will be able to make more changes, and so forth. The more substitutes each team uses, the closer the match becomes. In international matches, each player must be substituted off at the earliest possible opportunity. This allows the team time to react to any injuries that may occur during the game. In domestic matches, players are not required to retire from the game when they come out of the lineup. They can continue playing provided they remain on the field for less than twenty minutes without being replaced. In Major League Soccer, there are two ways teams can equalize the score: through a direct free kick or by using the advantage of geography. If the score is tied at the end of regulation time, both teams will advance to a single extra period called a "penalty shoot-out". On the first try, the team that scored will progress while the opponent will be forced into overtime.