"Trade kill in CS2, defined"

A trade kill is killing the opponent who has just killed your teammate, within a short window.

Trading is the mechanism that makes aggressive Counter-Strike survivable. A duel lost on entry costs the round only if it goes untraded; if the opponent is immediately killed, the numbers are level again and the map control taken by the entry frag is retained.

This is why positioning is coached around trade distance. Two players spread too far apart cannot trade each other, so every duel becomes a straight coin flip on a 5v5.

Trades are one of the four components of KAST — a player who dies but is traded still contributed to the round, and the stat records it.

Per-duel data, including who traded whom, is available through the CS2 data API.