American League East
Baltimore Orioles: The O's have some power, but they have major on-base issues, which makes it tough to put rallies together. They're 11th in the American League in on-base percentage, and they're currently without their top two providers of OBP, Nick Markakis and Jim Thome. They absolutely must hit homers to score runs, or keep winning a whole lot of 3-2 games.
New York Yankees: A team that once had seven starters now has ... well, fewer than that, for sure. Rotation depth has been a worry for the Yankees for much of the year, and it still is. If Andy Pettitte comes back strong, it will be huge for New York. CC Sabathia and Hiroki Kuroda have been rocks, Phil Hughes has been better than many people seem to think, but after that, it's a worry.
Tampa Bay Rays: Even with Evan Longoria's return, this just isn't a deep enough lineup. A pitcher who can neutralize Longoria and Ben Zobrist can usually shut down the Rays. You have to shut them down to beat them, of course, because of that terrific starting pitching, but it's just too easy to do that most days.
American League Central
Chicago White Sox: Chicago's bullpen remains a worry, with questions on the right and left sides. There are some intriguing arms here, and lots of options for manager Robin Ventura, but somehow, it seems the whole is less than the sum of the parts. Brett Myers has averaged less than a strikeout every two innings since coming over from Houston, so he hasn't been the solution the Sox hoped for.
Detroit Tigers: The heart of the lineup is potent, as are the front of the rotation and the back of the bullpen. One concern that Detroit can't get around is defense. The Tigers don't make a lot of errors, but that's because they don't get to a lot of balls. They rank 27th in the Majors in defensive efficiency rating, which is a simple measure of how many balls in play a team turns into outs.
American League West
Texas Rangers: OK, there's not a lot wrong here, but the catching position is an issue on both sides of the ball. There's a reason they acquired Geovany Soto, but he hasn't hit since coming over from the Cubs. Mike Napoli is having a down year as well, and Texas backstops have also had difficulty controlling the running game.
Oakland A's: The A's prevent runs, in large part because they're an excellent defensive team. What they don't do is strike people out. That's not necessarily a problem in the regular season, but come October, power pitching tends to win. The A's are 26th in the Major Leagues in pitchers' strikeouts, which makes them vulnerable to a bad defensive day or a good offensive opponent.
Los Angeles Angels: The bullpen situation has stabilized, but that doesn't mean it's been solved. The Angels' best middle relief, at this point, is their starting pitchers. When the starters don't go deep, it opens up a soft underbelly that's been exposed all year long. That can be less of a problem in October, when a team's top two or three relievers get a larger share of the work, but the Halos need to get there first.
National League East
Washington Nationals: Like Texas, the Nationals are one of the deepest and most complete teams around, but it remains to be seen how their rotation looks in the absence of Stephen Strasburg. Sure, it's an excellent unit, but any team is going to get weaker when you take away its No. 1 starter. The Nats should be fine, but their margin for error is assuredly less than it was.
Atlanta Braves: The bullpen has been brilliant, and unlike last year, it hasn't been overworked, so it should hold up until the end. The lineup is deep and effective. But as odd as this sounds, the Braves' rotation is a worry. Kris Medlen has been huge for them and Tim Hudson motors along, but Paul Maholm and Tommy Hanson have sputtered. Mike Minor, who has been sensational at times and shaky at others, is a big variable.
Philadelphia Phillies: In what is surely a surprise to anyone who's seen Citizens Bank Park packed for a big game, the Phils haven't been very good at home this year. Their 38-37 record gives them the lowest home winning percentage of any contender. Their hitters haven't taken advantage of the friendly dimensions at CBP, ranking in the middle of the pack in most offensive categories at home.
National League Central
Cincinnati Reds: Take the most dominant relief pitcher in baseball, maybe in years. Now mix in a case of "shoulder fatigue." Lefty Aroldis Chapman is dealing with a physical issue in his pitching shoulder, and that's a big worry. The Reds don't have a whole lot of weaknesses; they're a balanced and deep team. But Chapman is one of the keys to their success, and he's a question mark for the time being.
St. Louis Cardinals: The rotation is a big worry right now, even as the bullpen is finally getting sorted out. Jake Westbrook is out. Adam Wainwright is scuffling. Jaime Garcia struggles mightily on the road. For years, the Cards have been built to go as far as their starters take them. Right now, they're leaning on Kyle Lohse's career year and surprising rookie Joe Kelly, then wondering what else they have.
Pittsburgh Pirates: Unlike the Phillies, the Pirates are lost when they leave home. Their 30-40 road mark is the second worst of any contending team, better than only the Brewers. They've actually hit well away from PNC Park, but Pirates pitchers' composite ERA in road games is a grisly 4.56, fourth worst in the National League.
Milwaukee Brewers: Once again, Milwaukee just isn't a very good defensive team. Like the Tigers, the Brewers don't make a lot of errors. But like the Tigers, it's in part because they don't get to a lot of balls. Alex Gonzalez's season-ending torn right anterior cruciate ligament certainly contributes to the issues, but it also isn't a new problem at Miller Park.
National League West
San Francisco Giants: This is a team without many worries, but it's definitely worth noting that two key sources of offense for them in the first half aren't contributing much right now. Melky Cabrera is out, of course, due to a suspension for a positive drug test. But in addition, Pablo Sandoval hasn't been himself since returning from the disabled list, putting up a .222/.281/.263 line over the past month.
Los Angeles Dodgers: In short, the stars aren't hitting. Matt Kemp is hitting .174 with one homer in the past 30 days. Adrian Gonzalez is hitting .233 with a .296 OBP as a Dodger. Hanley Ramirez has nine homers but a .281 OBP over the past 30 days. The capacity exists for this to be a frightening lineup, but right now, the guys who should be leading the charge aren't getting it done.
Arizona Diamondbacks: The biggest problem with the D-backs may just be that it seems they should be better. There aren't really gaping holes here, and yet it adds up to a .500 team. One area that could surely be better is the starting rotation, where no one has been terrible but only Wade Miley has really been better than average. Hot streaks from a couple of starters would be awfully welcome.
There, now don't you feel better?