Search and Destroy, often abbreviated as S&D or SnD, and referred to as YOLO as an April's Fool joke  and renamed Looking For The One in Modern Warfare to celebrate Valentines Day 2020  is an elimination-based game mode that has been featured throughout the Call of Duty series. A one-sided game mode, the goal is for an attacking side to either eliminate the defending team or detonate either one of two bomb sites. Players only get one life per round, with most versions of the mode going to a best-of-seven rounds (first to four rounds wins). There is an intermission/half when two or three rounds are completed.
The mode is popular mainly due to its high XP potential; kills in Search and Destroy are typically worth five times that of in Team Deathmatch (50 points in Call of Duty 4: Modern Warfare and 500 in Call of Duty: Modern Warfare 2 and Call of Duty: Black Ops (1000 points for a headshot). Only 100 points are awarded in Call of Duty: Black Ops IIand most games after, due to the Scorestreak system, but 500 XP is awarded as a Medal called Elimination. No points are rewarded for a kill except by the way of a medal in any gametype in Call of Duty: Black Ops II and most games after, and the player can view these medals at the end of a game through the screen that pops up at the end of a match. On another note, the fact that players do not respawn until the next round could lead to long waits to play again, especially should the player die early into the round.
A Hardcore version has also been featured in Call of Duty 4: Modern Warfare and all other games onwards. Modern Warfare 3 Hardcore mode also features the "Ricochet" setting, where if someone tries to shoot or team kill a friendly player, all damage caused to that player will be inflicted onto the person who caused the damage. So essentially by trying to kill a friendly teammate the player will only kill themselves.
At the beginning of a round one team is assigned as the attacking team while the other is assigned as the defending team. There is a bomb located close to where the attacking team spawns, which can only be carried by one player at a time. The bomb is dropped on the ground when the player carrying it is killed. The timer starts ticking as soon the round begins. The team that wins four rounds (seven rounds in Call of Duty and United Offensive, six in Call of Duty: Advanced Warfare) first win the game.
After the first three rounds the two teams switch roles for another two rounds. If subsequent round(s) become(s) necessary the two teams alternate roles for each round.
In Call of Duty 4: Modern Warfare through Call of Duty: Ghosts, after the first three rounds, the two teams switch roles, and is termed as "Halftime". If both teams are tied at 3 wins each (meaning, the second three rounds have passed), an "Overtime" will be called, the tie-breaker round. Teams may or may not switch roles during Overtime, depending on which team has more kills. The team with the most kills will defend.
In Call of Duty: Advanced Warfare, Call of Duty: Black Ops III, Call of Duty: Infinite Warfare , Call of Duty: Modern Warfare Remastered and Call of Duty: WWII teams switch every round, similar to eSports rules.
Eliminate all enemies, or destroy an objective. Plant the bomb on one of two objectives, indicated by an A or B, then defend it until there is not enough time to defuse it. Note that the bomb can kill any nearby enemies, and the person who planted it. In the Hardcore Ricochet mode if a teammate is within the kill-radius of the explosion, and the player who planted is still living, if the bomb explodes it will kill the planter. If a player is able to plant the bomb during the last seconds of the given time limit, time is extended depending on the fuse time of the bomb (since the defending team has to defuse the bomb).
Eliminate all enemies, let time run out, or defuse a planted bomb. Remember that it takes 5 seconds to defuse the bomb on stock settings (7.5 seconds in Call of Duty: Advanced Warfare). Even if all enemies are eliminated after the bomb is armed, the attackers can still win the round if the bomb explodes. Victory is achieved as soon as the bomb is defused regardless of how many attackers are still alive. Defusing the bomb is very loud, and can be heard from quite a distance. If no bomb sites are destroyed, the defending team wins if the time limit is reached regardless of how many defenders and attackers are left alive. The defending team can also win if neither site is bomb-planted within the time limit, and at least one defender is still alive. A player should also note that when a bomb is planted the time limit is temporarily stopped until the bomb is defused or explodes.