Are football players allowed to screen the goalie? It gives them an edge. I know that in hockey players are allowed to screen but I'm not sure about football.
In general, players may stand between the goalkeeper and the ball to block their vision. However, there are two key instances where this would be illegal.
If a player is standing in an offside position when the ball is played by a teammate, they may not block the goalkeeper's (or for that matter any other opponent's) line of sight to the ball.
A player in an offside position at the moment the ball is played or touched by a team-mate is only penalised on becoming involved in active play by:
interfering with an opponent by:
preventing an opponent from playing or being able to play the ball by clearly obstructing the opponent’s line of vision
A player may not shield the ball if it is not in playing distance. For example, if a player stands in front of the goalkeeper on a corner kick, and then moves to prevent the goalkeeper getting around them, this should be called as impeding.
Impeding the progress of an opponent without contact
Impeding the progress of an opponent means moving into the opponent’s path to obstruct, block, slow down or force a change of direction when the ball is not within playing distance of either player.
All players have a right to their position on the field of play; being in the way of an opponent is not the same as moving into the way of an opponent.
A player may shield the ball by taking a position between an opponent and the ball if the ball is within playing distance and the opponent is not held off with the arms or body. If the ball is within playing distance, the player may be fairly charged by an opponent.
Earlier on it states:
An indirect free kick is awarded if a player:
- impedes the progress of an opponent without any contact being made
And in the section on direct free kicks:
A direct free kick is awarded if a player commits any of the following offences:
- impedes an opponent with contact
Screening goalies happens all the time, whether it's intentional or not. It's pretty likely that the player screening would be offsides, so any shots attempted would be whistled offsides anyways.
As Nicholas V. points out, a player screening the goalie is usually in an offside position, and also active when a shot at goal is taken, so it is not a useful tactic in open play.
The only times I've seen this done (at amateur level) are when a defender stands on the goal-line when defending a free kick. This means that an attacker can stand in front of the goalkeeper without being offside, and block his view of the ball.
Of course the screening attacker has to be aware of the defender rushing off the line before the kick is taken, leaving him offside.
There is some more information on this page about free kicks (in section Why Doesn't the Defending Team Put Players On the Goal Line?)