Americans may have incurred some 20.3 million sports-related injuries last year, but most of them were nothing more serious than a scraped knee or a bruised ego. According to a nationally representative survey of 15,063 Americans age 6 and older, conducted in January by Hartsdale, N.Y.-based research firm American Sports Data, Inc. (ASD), 53 percent of sports injuries are either self-treated or require no treatment at all. Only 17 percent of accidents result in a trip to the emergency room, ASD reports. Boys between the ages of 12 and 17 have the greatest risk of being injured. Although teenage boys represent barely 5 percent of the population, they account for 17 percent of all sports injuries and 23 percent of those requiring E.R. treatment. Ah, well. Boys will be boys.