FIFA said on Monday it would investigate a coin-throwing incident which halted Northern Ireland's World Cup Group Three qualifier against Poland for five minutes at Windsor Park on Saturday. Northern Ireland's 3-2 win, which took them to the top of the group, was marred when Swedish linesman Stefan Wittberg (pictured) was struck by the coin thrown from the crowd during the first half of the game in Belfast. In a statement on Monday, world soccer's governing body said: "FIFA are currently reviewing an incident in the World Cup qualifier between Northern Ireland and Poland on Saturday, where a Swedish assistant referee was hit by a coin. "FIFA has received a report from the match referee (Martin Hansson) as well as the match commissioner. "Following a review of those two respective reports, FIFA will then decide on whether any disciplinary procedures will be opened." The match was also marred by crowd trouble before and after the match with a number of police officers injured and nine fans, mainly Polish, arrested. A spokesman for Belfast police added: "Officers came under attack from bottles, bricks and fireworks. A number of fans, both Northern Ireland and Polish supporters, also received injuries. "Some required hospital treatment. We believe there was a hard core of Polish nationals who came to the game without tickets but with a very clear intent to cause trouble and disruption." Northern Ireland lead the group with 10 points from six matches, a point clear of Slovakia who have played two games less.