Battle of Tumhalad
The battle was fought as result of a massive Orc-buildup beneath the Mountains of Shadow and in the Pass of Sirion. Messengers from Círdan brought these tidings and a message from Círdan concerning a warning from the Vala Ulmo that the Elves of Nargothrond should not fight in open battles against the armies of Morgoth.
The Elves of Nargothrond, though, were not used to open battle for they had always waged a guerilla war, ambushing but never assaulting the forces of Morgoth. Also, the evil hosts were larger than anticipated and led by the Dragon Glaurung.
The forces of Nargothrond could not withstand the assault and were driven towards the plain of Tumhalad, were most of them, including King Orodreth and the Elf-lord Gwindor, were slain. Only Túrin withstood the attack of Glaurung, as he wore the Dwarven-crafted Dragon-helm of Dor-lómin.
The defeat suffered by the Elves allowed the Sack of Nargothrond by Glaurung.
Possible numbers for the battle are at least 30,000 Noldorin Elves, as Nargothrond had barely participated in th crushing defeat of the Nirnaeth Arnoediad. The army led by Glaurung must have been at least 70,000 if they could've defeated such a large Noldorin force, although it is likely that the presence of Glaurung contributed greatly to the elven defeat. Casualties for the Elves could've been as high as 25,000, with the remainder fleeing to Doriath, the Isle of Balar or possibly rallying to the defence of Nargothrond itself. Glaurung's army likely suffered heavy casualties as well, with possibly two thirds of the force being destroyed.