Athena made herself invisible.  Ares seeing only Diomedes broke off looting the body of Periphas whom he had killed, charged Diomedes, and cast his spear with deadly aim.  Athena deflected it.  Diomedes threw his spear and Athena rammed it into Ares waist and pulled the spearhead out again.

Ares roared in pain like ten thousand men, frightening the Greeks and Trojan men alike.

Ares retreated to Olympus and complained in his pain to Zeus.

Zeus called his son a two faced brute and most hateful of the gods and blamed the wounding on Hera.