Rules Quoted directly from IRB Rugby Laws
Quoted specifically with Reference to Illegal try by Wales Vs Ireland – 12 Mar 11.
Rule 19.2: QUICK THROW-INS
(a) A player may take a quick throw-in without waiting for a lineout to form.
(b) For a quick throw-in, the player may be anywhere outside the field of play between the place where the ball went into touch and the player’s goal line.
(c) A player must not take a quick throw-in after the lineout has formed. If the player does, the quick throw-in is disallowed. The same team throws in at the lineout.
(d) For a quick throw-in, the player must use the ball that went into touch. A quick throw-in is not permitted if another person has touched the ball apart from the player throwing it in and an opponent who carried it into touch. The same team throws into the lineout.
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(e) At a quick throw-in, if the player throws the ball in the direction of the opposition’s goal line or if the ball does not travel at least 5 metres to the 5-metre line along or behind the line of touch before it touches the ground or a player, or if the player steps into the field of play when the ball is thrown, then the quick throw-in is disallowed. The opposing team chooses to throw in at either a lineout where the quick throw-in was attempted, or a scrum on the 15-metre line at that place. If they too throw in the ball incorrectly at the lineout, a scrum is formed on the 15-metre line. The team that first threw in the ball throws in the ball at the scrum.
(f) At a quick throw-in a player may throw the ball in straight along the line of touch or towards that player’s goal line.
(g) At a quick throw-in, a player may come to the line of touch and leave without being penalised.
(h) At a quick throw-in, a player must not prevent the ball being thrown in 5 metres.
Sanction: Free Kick on 15-metre line
(i) If a player carrying the ball is forced into touch, that player must release the ball to an opposition player so that there can be a quick throw-in.
Sanction: Penalty kick on 15-metre line