While the TF2 Wiki does state:
A kill assist is awarded to a player dealing a fair amount of damage to an enemy before another team member finishes the enemy off.
It is ambiguous however. Many times I have damaged an enemy before another player comes to finish them off, yet the killfeed only shows that person who received that kill, and no assist points being rewarded to me.
Here's a sample scenario that happened to me over the weekend playing TF2 as a scout:
- I spot a Heavy enemy
- Heavy enemy spots me.
- I fire my Scattergun.
- He fires his Minigun.
- I die.
- Killcam reads "Heavy --> Me"
- Killcam reads "Heavy - 6HP"
- Pyro teammate runs up.
- Pyro incinerates Heavy.
- Killcam reads "Pyro --> Heavy"
What "damage" do I have to do in order for it to count as an assist? Is it a numerical value? Or a percentage of the target's hp?