I have been told that the flip throw in is illegal. The only documentation I have found to support this is on page 128 of the 2009-2010 Laws of the Game of the fifa website. This is what it says:
“If the ball touches the ground before entering the field of play, the throw-in is retaken by the same team from the same position provided that it was taken in line with the correct procedure. If the throw-in is not taken in line with the correct procedure, it is retaken by the opposing team.”
If a player tries the flip throw and the ball touches the ground in the process of delivering the ball, they simply retake with a “normal” throw. Is this correct?
USSF answer (September 8 2009):
No, none of the above applies in this case. Whoever told you the flip throw-in is illegal has likely been abusing illegal substances.
The text you refer to, part of the 2009/2010 Interpretations of the Laws of the Game and Guidelines for Referees, means that the throw-in is retaken by the opposing team if the ball, after being released by the thrower, touches the ground before entering the field of play. It has nothing to do with the flip throw-in, referred to by the IFAB and FIFA as the “acrobatic throw-in,” which is perfectly legal if performed in accordance with the requirements of Law 15.