Altuve has been one of the best surprise stories of the young 2012 season, busting out to a .979 OPS through April 25. The Astros were supposed to be one of baseball's worst teams, but it turns out that they have been a lot more fun to watch than anticipated. At the center of that is Altuve.
Altuve hit a slow tapper that got past the mound, but only barely. Brewers third baseman Aramis Ramirez charged in to field it, but couldn't get a good handle on the ball. Altuve was credited with a hit, because the play appeared to be difficult for Ramirez. The Baseball Info Solutions (BIS) database disagreed, and docked Ramirez for failing to make a relatively straightforward play.
BIS measures the trajectory, location and velocity of every batted ball to determine how likely it is that a play can be made by each fielder. We can then approximate how many hits defenses are taking away from or giving to a hitter, in our plus/minus system. An above-average defense might have a rating of +2, because they have taken away two more hits than an average defense. Conversely, a below average defense might have a -6 rating, as they have allowed six more hits than an average defense.
Altuve has been the recipient of a lot of defensive failures in April, en route to a .431 batting average on non-home run balls put into play by the hitter, familiarly known as batting average on balls in play, or BABIP. Other players have not had this same good fortune. The Kansas City Royals were a favorite dark horse pick in the AL Central this preseason, but have had a miserable month. In the middle of their lineup is Eric Hosmer, whose .786 OPS has disappointed. Hosmer has just a .204 BABIP, weighing his batting line down.
When we look at the differences between ball in play averages, there are two major factors to consider: the qualities of the batter (how hard and in what trajectory he is hitting the ball), and the qualities of the fielders. The difference between Altuve and Hosmer can largely be attributed to the defenses they are hitting into.