Jose Igleias and Jhonny Peralta present an excellent case study in the perception of the value of offense versus defense. Iglesias has hit better than expected, and Peralta fielded adequately. But most of Jose's value comes from defense, and most of Peralta's comes from offense. Has Iglesias' defense provided enough value to replace Peralta's bat?
Iglesias had big shoes to fill. Among all major league shortstops who qualify for the batting title (this excludes Troy Tulowitzki), Peralta is first in batting average, on-base percentage, wOBA, and wRC+. He is second in slugging percentage. His defense was fine having prevented 3.7 runs above average. Fangraphs totals this as worth 3.6 wins above replacement. In 104 games, that is .03 wins per game above replacement and second to Ian Desmond in the major leagues.
It is hard to provide as much value with the glove as with the bat. Andrelton Simmons is having an outstanding season playing shortstop for the Braves, and has saved two to three wins with his defense. Peralta's bat was worth more than Simmons' glove. There are just not as many opportunities to make exceptional plays in the field as there are plate appearances. Would you replace Miguel Cabrera with the best defensive third baseman in history, if he could barely hit?
Jose Iglesias was hitting well for the Red Sox and has continued to produce with the Tigers. He has little power, but is getting on base at an above average .343 rate. His defense has already saved 3.5 runs above average per FanGraphs, and the eye test says it has been more. His fWAR is 0.8 in 29 games, or .03 wins per game. Given the error in the ability for these numbers to measure value, Iglesias is providing comparable value to Peralta. And would the Tigers have won on Labor Day with anyone else playing shortstop?