<P> Like many original sabermetric concepts, the idea of a defensive spectrum was first introduced by Bill James in his Baseball Abstract series of books during the 1980s . The basic premise of the spectrum is that positions on the right side of the spectrum are more difficult than the positions on the left side . Therefore, the positions are easier to fill as one goes left on the spectrum, since the physical demands are less . A corollary to this is that, since defensive skill is at less of a premium on the left side, players at those positions must provide more offense than those on the right . Another corollary is that players can generally move from right to left along the spectrum successfully during their careers, but moving a player from left to right is quite risky . </P> <P> A retrospective analysis of the 130 - year history of baseball shows that the defensive spectrum shifted once . In the late 19th century and early 20th century, third base was generally considered to be more challenging than second base . This was because the double play was relatively uncommon in this period; thus, the third baseman, who had to field hard hit grounders and throw the ball 120 feet to first base, had a far more challenging job than the second baseman, who threw the ball 70 feet at most . Frequent bunting also meant that the third baseman would be more often challenged defensively . </P> <P> As a result, there were far more good hitters at second base than third (great - hitting early second basemen include Nap Lajoie and Rogers Hornsby), and the defensive spectrum was: </P> <P> First baseman--Left fielder--Right fielder--Second baseman--Center fielder--Third baseman--Shortstop--Catcher--Pitcher </P>

What is the most important defensive position in baseball