I had written the other day about the defensive spectrum in regards to Ron Hostetter's post about Royals prospects.
One of the interesting things about the spectrum is that it has not remained static over time. For example, in the first half of the last century third base was usually considered a more demanding position than second base. As a result, great hitters such as Rogers Hornsby, Eddie Collins, Frankie Frisch, Charlie Gehringer, and Nap Lajoie manned second while slick fielders like Jimmy Collins, Pie Traynor, Stan Hack, and George Kell were placed at third. Today of course, second base is considered a key defensive position, which is why it rates behind only catcher and shortstop while third base has drifted left past center field to the middle of the spectrum and is populated with more productive hitters like Mike Schmidt, George Brett, Matt Williams, and Chipper Jones.
To illustrate the changing nature of the spectrum the following graph shows the OPS of second and third baseman over time. It includes only those players who played more than 100 games at the position for each year. Note that the change in the relative defensive value of the two positions can be traced to the early 1950s when the small-ball of earlier years replete with bunting and chop hitting (which a good third baseman can impact) had all but disappeared. It's interesting to note that the gap between the two positions is once again closing. I chalk this up to the realization on the part of the many teams that second base may not be as important a defensive position as many baseball people once thought, resulting in more offensive-minded players such as Jeff Kent, Alfonso Soriano, Todd Walker, and Mark Bellhorn being slotted there.
This trend can also be seen by breaking down the OPS numbers by quarter century:
2B 3B Pct
1900-1924 704 689 102%
1925-1950 745 764 98%
1951-1975 691 762 91%
1976-2003 730 783 93%