In case it slipped your mind during the Christmas rush, January will mark the 10th birthday of that four-inch foam friend of furniture, that rainy-day mother's helper, that awakener of athletic fantasies, the NERF ball. That little spheroid has gained so much momentum bouncing through the decade that the NERF line of products now accounts for 15% of the total business of Parker Brothers, the largest proprietary board-game company in the world. Not many people know this, but if all the NERF footballs ever sold—a staggering 18 million—were lined up end to end, they would stretch from Boston to Denver, presumably without knocking over a lamp.

The legend of NERF began in early 1969 in one of Parker Brothers' testing laboratories in Beverly, Mass. A design firm in Minneapolis had submitted a model for an indoor volleyball game. Parker Brothers employees were trying it out when in walked Edward Parker, then the president of the company. Parker, who died in 1974, was a fun-loving guy, so one of the players just tossed the foam ball from the volleyball set at him. It would be nice to record for posterity that Parker caught the ball and shouted, "Nerf! We've struck gold!" but what he said was something like, "Forget the volleyball game, just market the ball." The rest, as they say in game biz, is history.

The name NERF was glommed from hundreds of suggestions made by Parker employees, and the company was reluctant at first to use it because it went against the grain of the firm's classier titles like Monopoly, Risk and Sorry. When NERF was introduced to the public in 1970, it was billed as the "world's first official indoor ball," but it was not an overnight success. Buyers for toy stores tended to be skeptical of something so simple—a little four-inch ball made of cut polyurethane foam that was firm enough to be thrown effectively in still air but squishy enough so that a NERF fastball couldn't crack a pane of glass. But slowly, by word of bounce, sales began to pick up, and by the end of the year four million NERFs had been sold. The original ball was followed by a slightly larger version called the Super NERF. It, too, was a bestseller. A disc jockey in Nashville created a fictitious NERF Ball League, complete with players, teams and divisions, and he included NERF League scores in each sportscast. NERF fans were pleased, and Parker Brothers was certainly not Sorry it took the Risk, because it soon had a Monopoly on indoor sports.

NERF really took off when the football version was introduced in 1972. Made of molded foam, the football is denser than the original NERF, but it still spares mom's favorite mirror. NERF footballs are the largest-selling football of any kind in the U.S., and all NERF items combined surpass the sales of the king of games, Monopoly. NERFs Baltic-to-Boardwalk success story has come to include basketballs, soccer balls, airplanes, rockets, spacemen, flying discs and NERFOOP, a miniature basketball-and-plastic-basket set that the NBA might want to look into for Darryl Dawkins.

A few professional athletes are counted among NERF's millions of devotees. Third Baseman Ken Reitz of the St. Louis Cardinals discovered the benefits of NERF in 1977. He would bring his then-teammates Pete Falcone and Hector Cruz over to his new house for a friendly game of NERF ball in the basement. Reitz credited the NERF practice with correcting his swing and helping him break out of an early-season slump: in May of that year he hit .366 with six home runs and 23 RBIs and was named the National League Player of the Month. Last year, though, Reitz temporarily lost the true spirit of NERF, and during a long plane delay he took part in busting up an airport lounge. Reitz apologized for his aberrant behavior. If only he had taken his NERF ball with him.

NERF has its serious side, too. The U.S. Air Force Tactical Air Command hangs NERF planes head high from the ceilings at its bases to serve as ever-present reminders to pilots to be wary of smaller, slower-moving aircraft. TAC officials say that the NERF planes can claim some small credit for the more than 40,000 collision-free flying hours that F-15 fighter planes have accumulated in the last three years. At 97¬¨¬®¬¨¢ apiece, they're a bargain in protecting the $15 million aircraft and their pilots.

Electronic beeping devices implanted free of charge in NERF balls by the Bell Telephone Pioneers of America have helped the blind to enjoy sports. NERFs can be found in physical therapy departments of medical centers throughout the country. NERFs played an important role in the Manhattan Special Olympics program by allowing the mentally retarded to have fun and gain confidence through success in sports. In addition, more than 600 recreation departments across the nation now conduct NERF Future Stars programs for youngsters. As part of the 10th-birthday celebration, there was a big Fixture Stars competition and party in Chicago on Dec. 15. to be followed by one in New York on Jan. 12 and another in Los Angeles come March.

And to think it all started with the wrong idea. Parker Brothers never has gotten around to making an indoor volleyball game.

Happy NERFday.