Every player is obliged to play the card of the same suit as the one that was first led to the trick, if in possession of one. Failure to follow suit constitutes a revoke.
Play a card of the same suit as the one that was led by the other player.
(v.) To play a card of the same suit as the led suit.
To play a card of the suit led to the trick. Each player is required to do this if able. If unable, they must play trump. Only when out of the suit led and trump may a player play anything they choose.
Play a card of the suit that has been led.