The ball’s contact point is outside the painted line. A player hooks it back. From the stand it looks obvious that play should have stopped, but the contact point is not the test in association football.
IFAB Law 9 says the ball is out when it has wholly crossed the touchline or goal line, on the ground or in the air. If some of the ball still overhangs the line, it has not wholly crossed it.
Picture the line extending upwards
Imagine an upright plane rising from the outside edge of the boundary. The entire ball must pass beyond that plane. A spherical ball can touch the grass beyond the line while a wider part remains above it. The same principle applies when the ball is airborne.
This is why a low, angled replay can mislead. It may show grass between the ball’s base and the paint without showing the ball’s full position relative to the boundary. A useful view needs the appropriate geometry, not merely a sharper picture.
The player’s feet answer a different question
A player standing outside the field can still play a ball that remains in play, subject to the other laws. The boundary decision concerns the ball, not whether the player’s boot or body is beyond the touchline.
Conversely, bringing the ball back over the line does not undo the fact that it already went wholly out. Once that has happened, the appropriate restart follows.
Crossing a goal line is not automatically a goal. The ball must meet the goal-scoring conditions, including passing between the posts and under the crossbar, with no relevant offence. A ball elsewhere across the goal line leads to a different restart.
During a live match, follow the referee’s decision rather than stopping because your viewing angle suggests the ball is out. When reviewing footage, ask whether it actually shows the whole ball against the boundary before declaring the decision simple.