Racquetball is a racquet sport usually played indoors in an enclosed court. Other variations of racquetball can be played on one, two, or three walled courts outdoors. Racquetball is an offshoot of squash, which is popular in the European countries. The racquets are shorter than tennis racquets and the ball is made of rubber. Racquetball is a fast and exciting game which has turned many players into hopeless, hardbodied addicts of the sport. Because of its starting and stopping characteristics, racquetball is not considered to be an "aerobic" sport by definition, although it definitely can contain an element of aerobic exercise.