Watch the below video and consider your ruling, along with the reasoning, before opening the analysis.
The ball is played through to the attacking player who beats all defenders. As the player is about to score, the defending player makes a tackle from behind. The defending player clearly denies an opponent an obvious goal scoring opportunity by tripping, which was an attempt to play the ball. As the defending player attempted to play the ball, the player should be cautioned and a penalty kick awarded.