I also have a goal kick. If what you said is accurate, the defender was trying to prevent the goal by kicking the ball. In that case he was playing the ball. The attacker fell over the defender's foot. It is not a case where the defender was attempting to trip the attacker. See advice to ref's on the laws of the game 12.4:
"Tripping or attempting to trip is an offense if it is clearly directed at an opponenet and causes the opponent to falter or fall. Players, however, may trip or fall over an opponent as the result of natural play and no infringement of the law has been committed."
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