It is playing by the rules. It is respect for your teammates and for you opponents. It is respect for officials and coaches. It is being on time to start the match, and not delaying the match as you play. It is good manners, courtesy, and friendly attitude, whether you win or lose.
Sportsmanship includes teamwork.
In tennis doubles, it is two players working together to win the match. The players practice together and help each other to learn skills. In practice they also learn how to use each other s strengths and backup each other s weaknesses. For the match, they plan a strategy that will lead to a match win. During the match, they cover parts of the court according to their plan, and talk encouragement to each other.