Final answer:
An opponent obstructing a goalkeeper from putting the ball into play is considered a foul and is penalized according to the sport's rules, often with an indirect free kick in soccer.
Step-by-step explanation:
When an opponent obstructs the goalkeeper or prevents them from putting the ball into play during a match, it is considered a foul. The specific rule depends on the sport, but in soccer, for instance, this action would contravene the laws of the game and the opposing team could be penalized, often with an indirect free kick. In other sports, similar penalties would apply for obstruction or interference with the goalkeeper.