Is it a foul in football if the ball is kicked up in the air towards two opposing players, and the one in front is backing into the one behind in readiness for the ball arriving?
If the player behind puts out a straight arm to stop the other backing into him is this a foul? Even if he doesn't push the other player, but just keeps his arm straight?
It comes down to "who had position first?" If you get into position to field the ball, then you are allowed to maintain it fairly.
Obviously, the referee's interpretation of the contact will not always be perfect. But generally, a player who gets into position to play the ball first can maintain the position so long as he does not do anything dangerous in the challenge.
In fact, you arre allowed to impede when the ball is within playing distance. If you look through interpretations of Law 12, it's spelled out:
Impeding the progress of an opponent means moving into the path of the opponent to obstruct, block, slow down or force a change of direction by an opponent 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.
So, again, the whistle in this case is often not blown because of impeding play due to an arm bar, but rather due to charging or pushiing which is considered dangerous contact.
I am not 100% sure on this but I think you are allowed to use your body to block the opponent from getting to the ball, likewise you your arm to avoid running to on another. But I don't think holding the player away by pushing him will be missed as a foul.
Next time you watch a game on TV check how defenders react to the situation when a long ball is kicked towards them. The attacker would typically try to control the ball by getting it on the chest or nod the ball to a teammate. If the defender holds his arm out without pushing the opponent he: a) risks a fracture in the outstretched arm, and b) he's not effectively keeping the opponent away since there is more space around the arm (the opponent may just take a step to right or left and still be close to the ball).
