I tried to find something from the official FIFA website for the 2014 World Cup and cards, but the best explanation I could find was here: http://www.socceramerica.com/article/38551/new-yellow-card-rule-good-for-the-game.html
2 Yellow cards in a game = immediate suspension from the remainder of the current game and automatic one game suspension in the following game
1 Red card = immediate removal from current game, automatic one game suspension in the following game, and review for possibly more games depending on the severity of the foul
There is one point in the World Cup tournament where all Yellow Cards are “wiped off” and everybody again has a clean slate. Before 2010, this happened following the group stage, the first 3 games. For the 2010/2014 WC and going forward, this happens after the quarterfinals round. The reason for the change is Yellow cards in the semi-final games will no longer cause a player to miss the championship games. Previously, a player could get a yellow in the knockout round, a yellow in the semis, and then have to miss out in the final. This was the case in 2002 when Michael Ballack, many considered Germany’s best player, was forced to sit out in the Championship game b/c of a yellow card in the semi-finals.
A player must now go 5 games without being carded 2 times to avoid being banned a game, whereas previously it was 3. By moving the “clean state” period to a later stage in the tournament, everyone without a red card will be able to play in the final, but it also means anybody with a yellow card must play cautiously through the first 5 games of the tournament.
I do think it encourages more goals, especially through the first period of the tournament, but I also think physical defending may not be as present b/c of players fearful of racking up cards. Yellow cards are given nearly every game to at least one player on each side. To go 5 games without 2 for a physical defender can be a lot to ask. Yellow cards are given frequently enough that I’ve even thought having yellow cards wiped clean after every match would be about right..
The 2006 Cup in Germany saw the most cards ever with 345 yellows and 28 reds in 64 matches, averaging nearly 6 cards per game.