It's very important that young athletes learn to be team players, recognize the contributions of others, and be a graceful winner or loser. While people mostly relate this topic to sports, it should also be taught in life situations where there is any form of competition.
It is also important to be a positive role model for your son. You can do this by complimenting other athletes, even if they had a tough game. They can be complimented for not giving up, for the good plays they made, and what positive teammates they are. Doing this in front of your son will show him the importance of positive teamwork, as well as demonstrate behaviors he should be exhibiting.
Part of the teaching with him should involve telling him why it is important to be a good sport. Other people will not want to play with him if he isn't a good sport; good sportsmanship will make him a leader on his team. Youth who are bad sports not only bring down the morale of the team, but they can sit on the bench as a result. In this regard, it is also important to partner with his coaches so they are also teaching good sportsmanship and reinforcing positive behavior.
You can also practice with him at home in order to work on acknowledging others. Play a game with him. When he makes a good play or wins a game, you can acknowledge his win. He must also acknowledge you when you win a game. If you are playing ball in the yard and he makes a good play, acknowledge his play; he should also do the same for you or anyone else that makes a good play. The more you practice the skill, the more he will be able to practice recognizing others.