Complex sentence: Right-handers can throw to their left--i.e., toward first base--with much greater ease than can left-handers, so virtually all second basemen, shortstops, and third basemen are right-handed.
Split into simpler sentences: Right-handers can throw to their left--i.e., toward first base--with much greater ease than can left-handers. So in practical terms, all second basemen, shortstops, and third basemen are right-handed.