What is the penalty obstruction in soccer?

Obstruction no longer exists as a foul or rule infraction. It was replaced by "impeding the progress of an opponent", and it occurs when a player intentionally screens (gets in the way of) a player that does not have the ball or the ability to immediately play the ball. Although rarely called due to its oft-trifling nature, the restart is an indirect free kick for the offended player's team at the spot of the infraction (regardless of the location of the ball at the time). Note that it is perfectly legal (and sometimes a good strategy) to screen the ball from an opponent so that it rolls out of bounds and gives the blocker's team a throw-in or corner kick.