Mount Uhud
As the battle heated up, the Meccans were forced to somewhat retreat. The battle front was pushed further and further away from the archers, whom, from the start of the battle, had really nothing to do but watch. In their growing impatience to be part of the battle, and seeing that they were somewhat gaining advantage over the Kafirun (Infidels) these archers decided to leave their posts to pursue the retreating Meccans. A small party, however, stayed behind; pleading all along to the rest to not disobey their commanders' orders. But their words were lost among the enthusiastic yodels of their comrades.
However, the Meccans' retreat was actually a manufactured manoeuvre that paid off. The hillside position had been a great advantage to the Muslim forces, and they had to be lured off their posts for the Meccans to turn the table over. Seeing that their strategy had actually worked, the Meccans cavalry forces went around the hill and re-appeared behind the pursuing archers. Thus, ambushed in the plain between the hill and the front line, the archers were systematically slaughtered, watched upon by their desperate comrades who stayed behind up in the hill, shooting arrows to thwart the raiders, but to little effect. So they suffered defeat in the Battle of Uhud.
However, the Meccans did not capitalize on their victory by invading Medina and returned to Mecca. The Medinans suffered heavy losses, and Muhammad was injured.
(source)