Racquetball is a racquet sport played with a hollow rubber ball in an indoor or outdoor court. Joseph Sobek is credited with inventing the modern sport of racquetball in 1950 (the outdoor, one-wall game goes back to at least 1910 in N.Y.C.), adding a stringed racquet to paddleball in order to increase velocity and control. Unlike most racquet sports, such as tennis and badminton, there is no net to hit the ball over, and, unlike squash, no tin (out of bounds area at the bottom of front wall) to hit the ball above. Also, the court's walls, floor, and ceiling are legal playing surfaces, with the exception of court-specific designated hinders being out-of-bounds.Racquetball is very similar to 40×20 handball, which is played in many countries. It is also very similar to the British sport racketball (see below for a comparison).Joe Sobek is credited with inventing the sport of racquetball in the New Britain Connecticut YMCA, though not with naming it. A professional tennis and handball player, Sobek sought a fast-paced sport that was easy to learn and play. He designed the first strung paddle, devised a set of rules, based on those of squash, handball, and paddleball, and named his game paddle rackets.In February 1952 Sobek founded the National Paddle Rackets Association (NPRA), codified the rules, and had them printed as a booklet. The new sport was rapidly adopted and became popular through Sobek's continual promotion of it; he was aided by the existence of some 40,000 handball courts in the country's YMCAs and Jewish Community Centers, wherein racquetball could be played.In 1969, aided by Robert W. Kendler, the president-founder of the U.S. Handball Association (USHA), the International Racquetball Association (IRA) was founded using the name coined by Bob McInerney, a professional tennis player. That same year, the IRA assumed the national championship from the National Paddle Rackets Association (NPRA). In 1973, after a dispute with the IRA board of directors, Kendler formed two other racquetball organizations, yet the IRA remains the sport's dominant organization, recognized by the United States Olympic Committee as the American national racquetball governing body.In 1974, the IRA organized the first professional tournament, and is a founding member of the International Racquetball Federation (IRF). Eventually, the IRA became the American Amateur Racquetball Association (AARA); in late 1995, it renamed itself as the United States Racquetball Association (USRA). In 2003, the USRA again renamed itself to USA Racquetball (USAR), to mirror other Olympic sports associations.Kendler used his publication ACE to promote both handball and racquetball. Starting in the 1970s, and aided by the fitness boom of that decade, the sport's popularity increased to an estimated 3.1 million players by 1974. Consequent to increased demand, racquetball clubs and courts were founded and built, and sporting goods manufacturers began producing racquetball-specific equipment. This growth continued until the early 1980s, and declining in the decade's latter part when racquet clubs converted to physical fitness clubs, in service to a wider clientele, adding aerobics exercise classes and physical fitness and bodybuilding machines. Since then, the number of racquetball players has remained steady, an estimated 5.6 million players.