USA Today (Sept. 23) -- A commonly held belief, reiterated from youth ball on up to the majors, is that the harder a pitch comes in, the harder it goes out. Alan Nathan, physics professor emeritus at Illinois, has studied baseball extensively and estimates that, when a hitter squares up a ball on the sweet spot, only about 15% of exit velocity is attributable to the pitch’s speed at contact - often 3-4 mph slower than as measured at release point - while the remaining 85% is generated by the hitter.