An estimated 350,000 athletes endure some kind of head injury while playing sports every year in the United States, and that's only counting the ones who lose consciousness after impact. Counting the rest of the dings, pings and "rung bells" that result in concussions, the total could be as high as 3.8 million. That's why concussions are, in the words of agent Leigh Steinberg, "a health epidemic, the consequences of which are a ticking time bomb that may not be seen in their totality for 10, 15 or 20 years." Steinberg and NFL Hall of Fame quarterback Warren Moon, who suffered the first of his half-dozen concussions at age 11, headlined a summit Friday designed to draw attention to the growing problem of concussions in sports.