Complex sentence: The reserve clause stipulated that a team had the first opportunity to sign a player after the length of the contract had expired and if the team chose not to offer a contract the player could try to sign with a team of his choosing.
Split into simpler sentences: The reserve clause stipulated that a team had the first opportunity to sign a player after the length of the contract had expired. If the team chose not to offer a contract, then the player could try to sign with a team of his choosing.