One Direction concerts get pretty rowdy! The boy band has had problems in the past with fans throwing objects at them onstage — remember when Harry Styles got hit in the crotch with a shoe? — but the fun times turned dangerous when Niall Horan was nailed with a thrown item right in his already-injured knee.

Earlier this year, the 20-year-old received a major surgery on his left knee that had him in recovery for weeks. Even now, months later, the Irish singer has had to take it easy onstage in order for his knee to continue healing properly.

1D shows are known for getting a little crazy (flashback to the dozens of fans who passed out at a show in Peru), but the insanity was brought to a new level last night on the second Amsterdam stop of the Where We Are Tour.

A fan threw something up on the stage and hit Niall right in his knee, hurting him so badly that he had to limp off the stage for a brief break. Yikes!

Niall wasn't the only one to be hurt, either. Harry was hit directly in the face by an unidentified thrown object at the same show.

Afterward, the blonde singer turned to Twitter to appeal to fans to quit throwing items at the band.

Poor Niall! We hope you feel better soon!