Skirmish in Balin's Tomb

The fight of Balin's tomb between the Fellowship of the Ring and the orcs of Moria took place in the Third Age. The cause of the skirmish was when Pippin accidently sent the skelaton of a long-dead Dwarf tumbling down a well. The sound alerted hundreds of orcs that now dwell in the mines.

The book
The orcs attack through the only door to the room of Balin's tomb. Aragorn and Boromir baracade the door. Arrows shoot through the cregs in the door. They eventually break through and the battle begins. About twenty orcs enter the room during the battle. The Fellowship fight them off, and then run to the bridge of Khazad-Dum.

The film
In Peter Jackson's film, there are an endless number of orcs attacking the Fellowship. Boromir, before the battle, realizes they have a cave troll with them. They continue fighting the orcs, and eventual the troll arrives. During the fight against the troll, Balin's tomb is destroyed. The troll's club is eventually smashed and it begins to use the chain around its neck as a whip. Legolas dodges the whip and shoots countless arrows at the creature. The troll soon turns its attention towards Frodo, who loses his weapon in the process. Aragorn comes to Frodo's aid and stabs the troll with a large spear. The troll knocks Aragorn unconscious. It then stabs Frodo with the very same spear Aragorn stabbed him with. Thinking Frodo is dead, Merry and Pippin leap on the creature's back. This distraction allows Legolas to shoot a perfect shot through the roof of the creature's mouth, instantly killing it. Frodo survives the troll attack, thanks to the mithril vest he was wearing. Before more orcs arrive, Gandalf leads the Fellowship out of Balin's tomb.