A trade veto is the mechanism a league uses to block or reverse a completed trade, usually when managers suspect collusion — two owners conspiring to strengthen one roster — or a clear mistake. Leagues generally pick one of three postures: no review at all, so trades process instantly; commissioner review, where the commissioner can reverse a trade only for collusion or error; or a league vote, where a set number of managers can veto.

Each posture trades one risk for another. Instant processing keeps the league moving but offers no recourse against a lopsided deal; league votes invite the opposite problem, where managers veto trades simply because a rival got better.

On Sleeper the commissioner holds ultimate control and can veto or force through any trade, and the league can also enable a vote-based veto with a commissioner-configured threshold. Which standard applies — “collusion only” versus “anyone can vote no” — is exactly the kind of rule that has to be written down before a disputed trade puts it to the test.