Sportsmanship in tennis means that the player calls the lines to the best of his/her ability, recognizes the other player when she/he hits an impressive serve or shot, wins without gloating, loses gracefully, and is friendly and respectful during the match, between side changes, after the match, and while watching other matches.  

The player does not participate in acts which are distracting, intimidating, dishonest or harmful toward the opponent, such as screaming on the court, excessive celebration, repeatedly questioning the opponent's line calls, cheating or other negative behavior.

The tennis player is also able to rise above his/her opponent's negative behavior by respectfully calling for an official or dealing with it in a positive manner without retaliating.  This is probably the hardest skill for a tennis player because the opponent is trying to cause harm to him/her and may actually be causing him/her harm, but this is an amazing life skill.  He/She is the better person!