BTS' Jin was hurt on stage.
BTS was performing in Busan's 'One Asia Festival' on the 23rd, and fans noticed that he was grabbing his ear in pain during the performance and again after, during their introductions. Some guessed that the fireworks had exploded too close to his ear and either the noise had hurt him or the sparks had gone to his ears. Others speculated that his earpiece might have malfunctioned and sparked in his ear, because he reacted a bit after the fireworks went off.
Hopefully if there was any injury, it was very mild.