Most human beings hate to lose. Some young kids take it especially hard. Yet losing some, like winning some, is a part of life. It's an important lesson for your child to learn, and it builds resilience and good sportsmanship.
Be sure your child knows that being a good sport means not complaining or getting mad if you lose. It also means not making fun of other players or players he perceives as causing the team's loss. Emphasize that after a loss, instead of anger, a better response is a vow to try harder next time.
Praise is a good way to reinforce graceful losing: "I saw how you went up to the other team's pitcher and shook his hand. I liked that." Don't completely belittle a loss or ignore it. Instead empathize and direct him to the future: "I bet you feel bad about losing today. That's okay. There's another game next week."
Above all, avoid criticizing or henpecking. Let it go. Sometimes parents fixate on a loss more than the child.
Don't replay the game: "What happened out there? Why didn't you…" Neither should you rebuke your child when he does show an emotional response to a loss. Being called a "baby" never made anybody feel better and never taught anyone a lesson.
Beware of your reaction to a winning situation, too. Don't let your child hear unsportsmanlike comments from you, such as "Boy, they were a bunch of losers, weren't they?" Or, "You guys wiped the floor with them!"
You swore you'd never sound like your mother, but then it slips between your lips: "Because I said so!" Or, "Because I'm the mother, that's why!"Such phrases are rarely effective – but they can make you feel better. And there's not a thing wrong with that, once in a while. As Mom always said, "When you're the mother you can make up the rules."