Obstruction, blocking, and crossing.

What obstruction means

Obstruction is foul play when a player illegally interferes with an opponent's chance to tackle, contest, or play the ball. In everyday language it is often called blocking, screening, or crossing.

• Blocking: a player deliberately gets in a defender's path to protect the ball-carrier or stop the defender reaching the ball.
• Crossing: the ball-carrier or a support runner changes lanes so that a team-mate becomes a barrier between the defender and the ball.
• Offside obstruction: a player in an offside position interferes with play, even if the contact itself looks minor.
• Dead-ball obstruction: players still cannot block or interfere with opponents once the ball is dead.

What players are allowed to do

Not every collision in a running line is obstruction. Rugby is crowded, and players are allowed to run support lines, receive passes, compete for possession, and hold a legitimate position on the field.

• A support runner may run a hard decoy line if they do not deliberately prevent a defender from tackling the ball-carrier.
• A player may stand or move in open play if they are onside and not using their body as an intentional screen.
• Players may bind and drive legally in a scrum, ruck, or maul, where contact with opponents is part of the contest.
• Shoulder-to-shoulder contact is allowed when opponents are genuinely running for the ball, but pushing or charging outside that contest can be penalised.

When it becomes a penalty

The key question is whether the player prevented an opponent from making a play they were entitled to make. Referees look at the running lines, the defender's realistic chance, and whether the contact or screen changed the outcome.

• A decoy runner who runs into a defender and opens a gap for the ball-carrier is at risk of an obstruction penalty.
• A ball-carrier who runs behind a team-mate and uses that team-mate as a shield can be penalised for crossing.
• A support player in front of the ball cannot block a defender from tackling the ball-carrier.
• An offside player who obstructs, screens, or interferes with play can be penalised even without a heavy collision.

How officials judge it

1. Identify who had the ball and where the potential blocker was in relation to the ball-carrier.
2. Check whether the defender had a realistic chance to tackle, contest, or move into the space.
3. Decide whether the attacking player changed line, held position, or initiated contact to stop that defender.
4. Ask whether the obstruction was material: did it affect the defender's ability to make the play?
5. Apply advantage if the non-offending team can still benefit, or award the penalty if the illegal block mattered.

Why crossing is different from passing

Crossing usually describes an attacking move where two players' running lines overlap. It is legal if the pass and lines leave defenders a fair chance to tackle the new ball-carrier. It becomes illegal when the old runner, a decoy, or another team-mate blocks the defender's path.

The ball-carrier also has a duty not to run into an offside team-mate to obstruct the opposition. If the defender is taken out by the team-mate rather than beaten by the pass or footwork, the referee may bring play back for obstruction.

Where contact is expected

Rucks and mauls create their own contest and offside lines, so some contact that would be illegal in open play is normal there. Players may bind, drive, and compete from legal positions, but they still cannot use the contest as a cover for side entry, offside interference, sealing off, or blocking defenders from in front of the ball.

This is why obstruction often appears near mauls. A player who is bound in and onside may be part of a legal drive. A player who detaches, swims around the side, or stands ahead of the ball-carrier to screen defenders may be penalised.

What fans often miss

• "He just stood there": standing still can still be obstruction if the player is in an illegal position and deliberately prevents a defender from playing.
• "There was no tackle anyway": the defender does not need to prove they would certainly have made the tackle; officials judge whether the obstruction denied a realistic opportunity.
• "Every decoy is illegal": decoy runners are allowed. They become illegal when they materially block or take out defenders.
• "The defender chose the wrong line": if the defender overreads the attack and runs into a legal support runner, that may simply be play on.
• "Only attackers obstruct": defenders can also obstruct opponents who are chasing the ball, supporting play, or trying to compete legally.

What the referee usually calls

The normal sanction for obstruction is a penalty to the non-offending team. If the obstruction prevents a probable try, the referee can also consider a penalty try and misconduct sanctions, but that depends on the specific sequence and level of foul play.

Officials often use the TMO for possible obstruction before a try. They look back through the attacking phase, identify the relevant contact or screen, and decide whether it had a material effect on defenders. Minor contact away from the ball may be ignored if it did not change the defender's options.

What this page covers

This explainer covers rugby union under the World Rugby law structure. Competition-specific referee directives can affect emphasis, especially around attacking mauls and pre-try reviews, but the basic principle is stable: players may compete for space and possession, not intentionally block opponents from a fair play on the ball.

Source material

• World Rugby Laws of the Game
• World Rugby Passport: Law 9
• World Rugby Passport: Law 10
• World Rugby Passport: Law 15
• World Rugby Passport: Law 16