The following steps are guaranteed to pass your legacy of poor sportsmanship on for generations.
Instill in your child the sense that regardless of physical ability, they by nature are simply superior to all other human beings.
This is best accomplished through a series of compliments like "you owned that kid," "he (or she) ain't got nothin' on you," followed up by a "whoooo" and an emphatic hand motion.
Be sure to correct opposing players in a loud, forceful manner, even when a simple discussion will do.
This is best accomplished by always keeping a rulebook on hand, with pages dog-eared to commonly misunderstood rules. Not only can you point to page 43, section 8b, but then you can throw the manual in a fit of rage, thereby demonstrating the appropriate behavior for your child to mimic.
Heckle opposing players about their skills, or lack thereof, even when you cannot perform the skill in question.
For example, if while playing basketball, the opposing player misses a layup, respond by saying "that was so easy, even my grandmother could make that shot." Follow it with a missed layup of your own, after which you question whether or not the basketball hoop is regulation height.
After a game is completed, be sure to make an underhanded remark.
For example, if you win, tell the opposing player "good game… at least by me," or "maybe next time I won't try so hard."
Just follow these four simple steps, and your kid is sure to be a winner. Remember, you don't even have to try that hard, your kid is always watching, judging, and eager to pick up on your behavior.
If you can't follow the steps, don't worry about it, you and your kids will just always be a losers. Whoooo!