You may have played the particular sport for a couple of years but you probably have teammates who are new to the sport. In order for your team to be successful you should encourage these newer or less skilled athletes so they can improve themselves and help the team. Making fun of them or giving them a hard time when they make mistakes is poor sportsmanship. Remember that you were just like them not too long ago. Probably not very good.
Good teams are teams where everyone works together to help each other.
Cooperation within a team is very important. This same attitude should apply to your opponents too. All too often we watch professional athletes and think that the way they behave during games is the right way to act. Unfortunately, that is not always true. You should really think about what you do and say during a game.