One of the first places I look now when a "surprise" team gets my attention is at the defense. This, I guess, is the big lesson from last year's Twins and Mariners, and a good thing to think about going forward. We can project pitching and hitting pretty well because our tools for handling past performance in those areas are sharp; it's harder to say from year to year which teams are going to have the best defenses because we can't say with certainty from year to year who the best fielders are. At the extremes, we're OK–Andruw Jones is good, Jose Canseco isn't–but there's a big middle ground in between, and knowing who's having a good season with the glove in May is less simple than knowing which hitters are shocking us.
That's a long-winded way of saying that during a season, I'm most comfortable evaluating defense at the team level, and doing so by addressing the basic question of defense: when a ball is put in play against a team, how often does that team turn it into an out? There are things this won't catch–outfielder and catcher arms, double-play efficiency, fielding errors–but it's a good quick'n'dirty method for evaluating defense, especially range.
Calculating this is easy, as it is basically the inverse of hits on balls in play: 1-((H-HR)/(AB-HR-SO)). Here are the rankings through Sunday's games:
American League National League Team DE Team DE
Red Sox .761 Dodgers .748 Yankees .745 Giants .742 White Sox .718 Pirates .724 A's .713 Mets .723 Mariners .708 Padres .719 Twins .707 Brewers .718 Royals .699 Reds .712 Rangers .699 Braves .712 Angels .699 Marlins .698 Orioles .691 Cubs .695 Devil Rays .681 Cardinals .693 Tigers .680 Expos .690 Blue Jays .675 Rockies .688 Indians .669 Diamondbacks .686 Phillies .684 Astros .670
A look at this list, especially the National League one, gives us a good idea at how some of the more surprising teams in the game are getting it done. The Red Sox' figure is off the charts–the Mariners led the AL last year with a .735 DE score–and seems to indicate that the defensive upgrades at second base and in center field, where Rey Sanchez and Johnny Damon now roam, have had a significant impact.
In the National League, the success of the Pirates and Giants–teams whose run prevention doesn't seem to match what their pitching has been doing–is in large part due to their defense. The Dodgers also seemed to have seen some benefit to adding Brian Jordan and Cesar Izturis to their defense, both improvements over Gary Sheffield and Alex Cora.
At the other end of the spectrum, the disappointing starts of the Blue Jays, Tigers, and Astros are reflected in their defensive performance. The Tigers, of course, are starting a bunch of utility players, converted catchers, and DHs, so perhaps this isn't a surprise. The Astros, however, have to be concerned that a staff which is in the middle of the pack in strikeouts isn't getting much help from the seven guys in the field. A questionable up-the-middle defense of Craig Biggio, Julio Lugo, and Lance Berkman is a weakness they may not be able to afford. Calls for the return of Adam Everett may make more sense than appears at first glance.
Contrast the Astros with the Diamondbacks, who lead the world in strikeouts, thanks to the duo of Randy Johnson and Curt Schilling as well as a relief corps that gets more than its share of Ks. While they haven't performed well defensively, they see fewer balls in play than most teams, minimizing the damage. The D'backs, of course, are 16-9 and tied with the Dodgers for first place in the NL West.
We're still not out of April, so these numbers have to be taken with a grain of salt. But if you're looking for an explanation as to why some teams are keeping runs off the board, while others are giving them up at a frightening rate, it's a good idea to look past the pitching staff and at the defense.