That's not really the case. Run production and run prevention are equally important. The thing is, at the major league level, the vast majority of run prevention occurs on the mound, as the difference between the best and worst major league fielders at a given position is relatively small, especially when compared to the difference between the best and worst hitters at the same position. So, when choosing a player, defense should be given some consideration, but much more consideration should be given to his offensive skill set, as that's where he's much more likely to be beneficial, with very rare exception. Warp's post sums it up. Defense matters, but when choosing between two second basemen or two centerfielders, ot two third basemen, or two catchers, the difference between the better hitters is likely greater than the difference between the two defenders. So, when making a choice, I'm likely to look only at offensive production. Moving players to a new defensive position throws a monkey wrench into the whole thing. While in lower levels of baseball, there is a greater descrepancy between defenders and bad defense often makes a larger difference in games. By the time players get to the major leagues, they likely are able to handle the defensive position which they man. If you gave me two players with similar offensive production and one is a better defender, I'd obviously take the better defender. But, on the other hand, if there are two players, one is a better defender and the other is a better hitter, I'll go with the better hitter almost every time. Now, if it involves moving a player out of position, then I might hesitate to take the better hitter over a player out of position.