What happens if…
The referee must resume the game after the half-time interval without changing sides and play the correct time of the first half. The teams then change sides, and the game is restarted with the kick-off for the second half.
The half ends when the referee stops play for an offence by the attacking team or when the ball:
goes into the goal
stops moving (including being held by the goalkeeper)
rebounds off the goalkeeper, goalpost(s), crossbar or corner flagpost and has no chance of going into the goal
goes out of play
is touched after the kick by any player (except the defending goalkeeper)