There's been an interesting discussion at Baseball Think Factory's Hall of Merit about replacement level under different one-big-number systems of rating players. You can read it here starting at post 39. One of the debaters, DanR, has been suggesting for some time that the replacement level for shortstops was very low in the early 1970s, which is another way of saying there weren't many good shortstops then. You can read in that thread a suggestion of why that might be.
Anyway, DanR has one method, derived from Baseball Prospectus' erstwhile contributor Nate Silver, and Tom Tango, of The Book Blog (see sidebar), suggested that as an alternative one might take anyone who wasn't in the top 50 playing at a given position as 'replacement-level players'. I thought I'd try a real example of that.
So I adjusted this on the principle that 50 suited the 30-team major leagues of today, while 42 would be better for the 24-team major leagues of 1972. Then I got the 43rd through about 96th ranked shortstops in terms of putouts (should have used assists, but I have an excuse), and calculated their wOBA (weighted On-Base Average). Then I made a similar list of the top 42 at second base and third base, and took those people out of the shortstop list. Then I aggregated the shortstops' batting by individual leagues and overall. Here's what I got:
NL replacements .274
NL regulars .263
ML regulars .262
AL regulars .260
ML replacements .257
AL replacements .243
These replacements in the NL are guys who don't have more than 85 at bats, and include people like Larvell Blanks, a 22 year-old utility player with a .355 wOBA who actually was more of a secondbaseman, but got 30 innings at shortstop. Or Craig Robinson, Larry Bowa's understudy at Philadelphia, with 16 assists and a .235 wOBA or Rafael Robles, who split time at third and short for San Diego, who also managed 16 assists but only a .150 wOBA.
Just looking at the list, I suspect the number would be closer to the AL level if it hadn't been for Blanks and another Brave, Gil Garrido, whose .302 wOBA in 75 at bats means that between them these two count for a little over 20 per cent of all replacement at-bats at shortstop in the 1972 NL.
EDIT: I meant to say something about the Braves' full-time shortstop, Marty Perez. He managed a below-avera wOBA of .247, and his TotalZone fielding runs were -14.8. He was only 25, though, and did manage to improve with both bat and glove after that, although he got moved to second in 1974.