Background:

The Quraish wanted to avenge their defeat in the battle of Badr as many pagans had lost their relatives in that encounter. After Abu Jahl's killing in the battle, Abu Sufyan became the new military Chief in Makkah. He was encouraged by all to rise an army against Madina. Kab bin a-Ashraf, the Jewish poet instigated many tribes against the Prophet (P B U H).
Events:
Abu Sufyan raised an army of 3000 troops with 300 camels, 200 horses and 700 coats of mail (armour). Women of families of the slain chiefs were also included. Hind bint Utba (wife of Abu Sufyan) was in charge of the women; Umm Hakeem, Grand daughter of Abu Jahl, and Fatima, sister of Hazrat Khalid bin Walid were also taken. The left and right flanks were under the command of Ikrima bin Abu Jahl and Khalid bin Walid respectively, while Amr bin Al-As was the commander of the cavalry. This army reached north of Madina in March 625 AD (Shawal 3 AH) and camped near the Uhad Hill on the road to Syria.

the Prophet (P B U H), in the meantime, had consulted his advisory council (Shura) and accepted the decision of the majority. He was able to recruit 1000 troops and left for The Uhad but on he way, the chief of hypocrites, Abdullah bin Ubay deserted with his 300 troops on the excuse that their houses were unsafe back in Madina. the Prophet (P B U H) camped with 700 troops on the Western slope of Uhad mountain. He appointed 50 archers under the Hazrat Abdullah bin Zubair (RA) on a narrow passage at the back of the Muslim army. They were strictly instructed not to leave unless ordered by the Prophet (P B U H). The Quran mentions the Prophet (P B U H) strategy as, "Remember that morning you left your household to post the faithful at their station for the battle". The right wing of Muslims was under the Hazrat Zubair (RA)and the left wing was under the Hazrat Mundir bin Amr.

As usual, the Quraish challenged for single combats. Hazrat Ali (RA)  and Hazrat Hamzah (RA) killed Uthman and Talha from the pagan army. With this, the general battle began, Muslim attack was fierce and Quraish began to retreat. Muslims continued to press the enemy and began to collect the spoils. When 50 archers saw this, most of them (35 or 36) also left their position and began to collect the booty. The Quran refers to these Muslims in these words: "When you with His (Allah's) permission were about to annihilate your enemy until you (archers) flinched and fell to disputing about the order and disobeyed it"  (3:152 Al Imran).

Khalid bin Walid quickly mobilized his troops and attacked through the passage vacated by the archers. This changed the scene and retreating makkans also made a counter attack as they saw Khalid bin Walid's powerful attack on the Muslims. Many Muslims were killed including Hazrat Hamzah (RA) who was martyred by Whashi bin Harb, who was asked by Zubyr bin Mutim to do so. Hind mutilated the dead body of Hazrat Hamzah (RA)  by chewing out his liver. In the panic, Prophet (P B U H) was also wounded and it was rumoured that Prophet (P B U H) was martyred. This disheartened the Muslims but soon Hazrat Kab bin Malik identified the Prophet (P B U H) who was surrounded by his close companions and taken to safety. The makkans in the meantime had martyred 70 Muslims and left for Makkah challenging to fight the next year.

Conclusion:

The Prophet (P B U H) has lost one tooth and his face was also injured. He, however, reorganized his army and began to bury the martyred Muslims. The Quraish list only about 20 to 24 soldiers.