Ball hits the referee: when does play stop?
Not every deflection from an official requires a dropped ball.
Contact alone does not stop play
IFAB Law 9 says the ball normally remains in play when it touches a match official. The exception requires the ball to remain on the field and one of three effects: a promising attack starts, it goes directly into goal, or the team in possession changes.
A hypothetical harmless deflection with the same team retaining possession and no promising attack is not automatically a dropped ball simply because the referee was touched.
The effect changes the restart
When one of those specified effects occurs, play restarts with a dropped ball. An official-contact deflection directly into goal is therefore not an ordinary goal to add to the scoreboard.
If the ball instead leaves the field after hitting the official, the remain-on-the-field condition is absent. IFAB's examples explain that the usual throw-in, goal-kick or corner restart applies based on the players' last touch and exit location.
Other rebounds can remain live
A rebound from a post, crossbar or corner flag that stays on the field remains in play under Law 9. Those contacts are different from the specified official-contact effects.
The ball is also out of play when it wholly crosses a boundary or the referee stops play. That whistle matters: an apparent finish after play has already stopped cannot simply be counted because the ball entered the net. Watch the reported restart alongside the score.