Principles of Attack
Penetration - The goal of the game is to score more goals than your opponent. You (or your teammates) must Penetrate the opposition's goal. To do this, you have to Penetrate their Line of Defense. You can Break Their Line of Defense by Passing, Dribbling or Shooting.
Support - Players who contribute to an attack provide Support. Teammates who are there to combine with the 1st Attacker (the player with the ball) are providing Support. Even if the 1st Attacker chooses to go alone, it often helps to have 2nd Attackers (in close proximity) and 3rd Attackers (further from the ball) making runs and dragging an opposing defense out of position to create space.
Width - Opposing defenses want to stay compact / connected, . . . they want to provide Cover for each other. When an attacking group creates Width in their attack, opponents are forced to choose between staying close to their teammates or tracking opponents and creating gaps in their own defense.
Mobility - To provide Support and create Width, player must be Mobile. They best attacking runs are made ahead of the ball. When players run from side to side or behind the 1st Attacker, they don't as easily draw the attention of opponents. When they run ahead of the ball, they become a larger threat and Defenders have to chose whether or not to follow them.
Improvisation - The best Defenses or very organized and prepared for everything teams typically throw at them. When the plan doesn't work, Attackers have to Improvise. The best attacking players can attack in many ways, but just do what needs to be done when the situation arises, . . . this is often something that wasn't covered in training.
Principles of Defense
Pressure - Individuals (the 1st Defender), blocks of players and entire teams can provide Pressure on opponents. Some teams employ a three second rule (or 5 seconds) to win the ball back after giving up possession. Sometimes teams wait until an opponent moves in to the Midfield or even the defending team's defensive third before Pressing. It's not uncommon for teams to immediately Press, drop off if the opponent breaks Pressure, then patiently wait until a mistake is made to win the ball back.
Cover - Cover is typically provided by 2nd Defenders. This is provided when a player put herself in a position to Press if the 1st Defender is beaten, but also defend the space behind the 1st Defender, . . . even to mark opponents in the space near the 1st Attacker. A good Defender expects the worst, is aware of potential problems and puts herself in a position to help in as many ways as possible.
Depth - Typically, players providing Cover do so with an appropriate amount of Depth. If players are caught "flat," on the same "line," or just too close to the 1st Defender, the opponent can beat both the 1st and 2nd Defenders with a well-timed pass or confident dribbling. It's safer to keep opponents in front of you.
Balance - If too many players get caught in the same area, an opponent can break down a defense by moving the ball quickly into another (more dangerous area). It's important that defensive groups stay compact, without becoming too concentrated in one space. Doing this effectively is described as being well-balanced.
Compactness / Concentration - Especially keeping in mind that a key Principle of Attack is Width, defensive groups most be sure to never get too far spread apart. Without becoming un-balanced, defensive groups want to stay compact and hard to break down. Defenders staying close to each other can Press opponents as they pass the ball from one to another, while prviding Cover for each other in case a teammate is beaten. They can close space quickly to cut out opposing passing lanes or block shots.