How many yellow cards does a player need before getting suspended?
Rules concerning game suspensions for yellow card accumulation are the same through the group stage and knockout stage of the World Cup, but are slightly tweaked for the semifinals and championship.
If a player receives two yellow cards over the course of the tournament, he will be suspended for the next game. If the player's first yellow card came in the group stage, it will still carry over to the knockout stage and the next yellow card for that player will result in a one-match suspension.
Players who accumulate two yellow cards in one game are taken out for the remainder of that match and they cannot be replaced, meaning their team will be the rest of the game a man down. That player is then suspended for the next contest, but the team will start that match with 11 players. It is the same if a player receives a straight red card.
For the teams that reach the semifinals, their yellow card count is reset to avoid a player getting suspended for the final through yellow card accumulation. A player would have to get two yellow cards or a red card in a semifinal game to get suspended for the final.
However, a player can still be suspended for the semifinal if he accumulates two yellow cards prior to that game, but he would be eligible for the third-place game or championship. For example, Brazil's Thiago Silva was suspended for the semifinal match against Germany in 2014 due to yellow card accumulation, but played in the third-place match against Netherlands.