Pretty bad. Hitting can make up for a multitude of sins, especially at first base. There's a reason that first base has been the home of the immobile slugger going back to the days of Big Dan Brouthers. With most hitters being right-handed, grounders are often directed to the right side of the infield. On most plays the first baseman's job is to stay around the bag and receive the ball, so their opportunity to do real damage isn't the same as the shortstop's. Assuming that a first baseman fits the offensive profile of his position, if he lacks Keith Hernandez's ability to come in on a bunt or Don Mattingly's range in the hole he should still contribute enough with the bat to make his lack of defensive ability a minor concern

Jason Giambi stretches this argument because he's not even a good receiver. While he scoops the occasional low throw, his vertical leap is purely hypothetical, and most everything thrown over his head seems to get by. Plays off the bag don't happen. We're talking about a first baseman who is not just bad, but might possibly be the worst defensive first baseman in the game. His defense was so bad that it contributed to runs that cost the Yankees a total of one win over the cost of the season (remember, it's not easy to lay causality for a win or a loss at any one player's door; the best we can do is look at run elements and see how things add up over the course of a season to get a better understanding of a player's abilities). That doesn't sound like a lot, but keep in mind that Giambi played only 68 games at first.

Baseball Prospectus's WARP (Wins Above Replacement), which considers both offense and defense, says Giambi was worth about six wins above replacement to the Yankees last year. That includes the loss created by his defense. Had he played at first on a daily basis, his defense might have started to eat into his overall productivity. Giambi still would have been a net positive, but his overall value would have been severely reduced

Posted by Rich:

It doesn't matter. First basemen aren't selected to the HoF on the basis of their defense.