Defending an internationally sanctioned Black Sea convoy

Would a NATO warship shooting down a Russian missile aimed at a Ukrainian cargo ship be an act of war?

Not necessarily if it were defending an internationally sanctioned convoy, but multiple missiles and uncertain targeting would create a dangerous escalation zone.

Shooting down an incoming missile differs from attacking the aircraft or ship that launched it. Under a United Nations, European Union, or NATO-sanctioned food convoy, interception could be framed as defence of protected shipping rather than an offensive act. The danger grows when several missiles enter a mixed formation of escorts and merchant ships because their intended targets may be unclear. A strike that hits naval escorts could itself be treated as an act of war, making rules of engagement and identification central to convoy protection.