A man struck in the head by a metal pin that rolled out of the centre field scoreboard at Wrigley Field earlier this week was apparently spared more serious injury by a plastic bucket he was wearing on his head, according to police and the Cubs.

The mishap occurred on Tuesday night during the Cubs game against the Arizona Diamondbacks. The pin, "rolled out of the scoreboard when the (score) tile was being changed," said Cubs spokesman Julian Green.

The hand-operated centrefield scoreboard at Wrigley has been in use since 1937. Green said the team has had no problems like this before.

Lucky escape: Cubs fans at Wrigley Field. Credit:AP

The 19-year-old man who was hit was taken to Illinois Masonic Medical Centre and received five staples to close a cut on his head, Green said.