Why does Bilbo miss most of the action in the battle of the five armies?

Bilbo misses most of the action in the Battle of the Five Armies because he is knocked unconscious during the fight. He is struck on the head by a falling rock, which renders him unable to participate in the battle. When he wakes up, the battle has largely concluded, and he learns about the events that transpired while he was out cold. This absence highlights his role as an observer rather than a direct participant in the conflict.