Watch the kick rather than the area boundary
Under Law 16, a goal kick is in play once it is kicked and clearly moves. Opponents must be outside the penalty area until then. The penalty-area line is therefore not a second activation gate that the ball must cross.
Suppose a goalkeeper passes four metres to a centre-back standing inside the area. The defender’s location alone does not make the restart invalid. The useful sequence is the ball’s movement, followed by the opponent’s entry, rather than the ball eventually crossing the large rectangular line.
Why pressure can arrive so quickly
A wide broadcast shot may show an attacker sprinting into the area almost as soon as the keeper passes. Compare the attacker’s position at the instant the ball first clearly moves. Entering afterwards is different from already occupying a prohibited position at the restart.
This timing explains why a short build-up can produce an immediate interception without the ball ever leaving the area. It does not establish that any particular clip is legal: an obstructed camera may hide the starting position. For a clear replay, keep the opponent and the stationary ball in the same frame, then advance to the kick. That is more revealing than following only the receiver’s first touch.
Questions answered
Must the ball leave the penalty area first?
No. The current activation point is the kick and clear movement.
Can a defender receive the goal kick inside the area?
Yes; being inside is not itself a restart offence.
Sources & further reading
Official references for the subjects discussed. Service terms and device software can change.