Wow. That is an impressively set up arena battle. What happened?
First volley
(It injures a lot in the front ranks of both sides - but they just step over the fallen and continue to advance, Kobold front ranks noticeably suffer due to the biconcave surface whilst the human casualties are limited to the tip of the formation).
Kobolds attack a legendary vampire warlord and his body guard - they all have either a dagger or a single steel bolt to fire.
After a couple dozen (around 30 or so) more volleys, it's over.
No one isn't injured except maybe 4 of the Dwarf lords who fought among the Kobold ranks. Dem martial trances. Biconcave formation works well for assaults apparently. Every casualty could be safely ignored by the masses. The battle went on for so long, some of the Kobolds from the first volley had actually recovered and got back up to continue fighting... Not very well admittedly, but a valiant effort. The human guardsmen in the front ranks fell shockingly quickly, and though their champions fought well, superior numbers either drove them back or killed them outright.
Brutality. The humans above only lost because they ran out of ammo. The vampire lord attacked by the Kobolds took out all of the attackers - sustaining major injuries, and most of his bodyguard was slain or critically injured, having fallen down far. The vampire lord however escaped underground, fleeing before any Kobolds or Dwarves caught sight of it.
In the tower on the left, nearly all of the humans within rushed out to fight off the Dwarf and Kobold assault in a last ditch attempt to save the fortifications, and while the counter attack was effective, the true damage was done by the commanders in their black bronze armour who stayed within and fought the invaders from the high ground with morningstars in hand.
A Pyrrhic victory to the Dwarves and Kobolds.