A throw-in is awarded when the entire ball goes across the touchline.  An opponent of the team who touched the ball last throws in the ball at the point at which it went out of bounds.  The object is to maximize territorial gain while ensuring that a teammate can gain possession from the throw.  A player should collect the ball and get into position as quickly as possible after the ball goes out of bounds in order to take advantage of teammates who might be breaking away toward the goal. 

To do a legal throw-in, the ball must come back over the head (referees usually look to see if the ball goes back past the ears) before being thrown forward; the ball must be thrown with both hands on it, and it must be released immediately after passing the front of the head (no spiking is allowed); both feet must be in contact with the ground when the ball is released; both feet must be behind or on the touch-line; and no twisting of the body is allowed to propel the ball further.  There are two basic ways to do a legal throw-in. One is to step forward with one foot in the direction of the throw, and drag the toe of the trailing foot as the ball is thrown. The other is to simply stand with both feet firmly planted and throw the ball in. Both ways are effective … which style is used is a matter of player preference. 

Here are the fundamentals of a proper throw-in, from 'The Nose to The Toes': 

1. Secure the ball with both hands, ensure that the index fingers and thumbs are as close as possible (almost forming a "W" or "U" shape with fingers on the ball).  Fingers should be spread to maintain control of the ball. 

2. Bring the ball over the head behind the ears with your arms loose and elbows bent and flared out. 

3. Stand with your feet a little more than shoulder-width apart with one foot in front of the other (start at a standstill first, then add 1 step, then 2, and so on).  If you prefer, place your feet parallel, shoulder-width apart. 

4. Face the pitch. 

5. Bring your head, neck, shoulders and trunk back, bending at the knees. 

6. Thrust the ball forward resulting in your entire body going forward.  Parts of both feet must remain on the ground at all times, behind or on the touchline. 

7. Release the ball as it just goes past the head. 

The throw-in is a pass … therefore, it should have all the characteristics of a pass (played to a teammate with the proper pace so that it can be controlled easily and possession can be maintained). 

The most common error in throw-ins is lifting the foot. This error almost always occurs because the player is trying to throw the ball too hard, and almost always occurs in players who use the method of putting one foot in front of the other … they lift the dragging foot in an unconscious effort to get more power on the ball.  If you notice you are lifting the foot repeatedly, switch to doing throws by standing with your feet together.  Your main job is just to get the ball on the pitch. By taking the pressure to set distance records off, your chances of a good throw are greatly improved. 

Tactics: 

• Scan the pitch while collecting the ball.

• Look for an open teammate.

• Throw the ball quickly, to keep the opponents off balance.

• Throw the ball where you will get the greatest territorial gain.

• Throw the ball so that it is easy for a teammate to control.

There are three important rules to remember:

1. A goalkeeper may not catch a throw-in.

2. There is no offside on a throw-in.

3. No goals may be scored by throwing the ball into the goal directly from a throw-in.

Note: If the ball does cross the line directly from a throw in taken by the defending team, it is a corner. If the throw is taken by the attacking team, the referee's decision should be 'goal kick'.

Sources: 

• Soccer-Coach-L Coaching Manual Collective

• Goal!  The Ultimate Guide for Soccer Moms and Dads”  (Averbuch and Hammond)

• “Coaching Soccer:  The Progressive Way”  (Ditchfield and Bahr)