Do enough preview pieces, and you start to run into issues of keeping the format fresh and interesting, both for the readers and for yourself. For my second-half preview, running today and tomorrow, I’m going to do something I don’t do often, which is use it to review my previous work. I often get requests to look back at my own predictions and explain why I was wrong about something (never to explain why I was right, I’m afraid), and I try to restrict that to one piece a year. The idea is that I’m writing about baseball, not about some guy’s predictions, and I think you can unconsciously get into some bad habits if you self-check too much.

For this project, though, I’ll refer back to my pre-season rankings, check and see how each team is doing relative to them, and look ahead to their second halves. As usual, I’m less concerned with record and more with runs scored and allowed (conceding that scheduling issues and the valances of partial-season fortune can play with those numbers a bit).

#30: San Diego Padres (me: 611 RS, 792 RA; projected: 615 RS, 817 RA). Down Jake Peavy, Brian Giles and their second-best hitter this year in Scott Hairston, the Padres now have the worst run differential in baseball, worse than even the Nationals, and the third-worst record in baseball. Given the competitive environment, the talent on hand and the upper levels of the farm system, the Padres need to move in the direction of rebuilding. That means trading Heath Bell, trading David Eckstein, and, yes, trading Adrian Gonzalez (now hitting .250). Of the 46 players who have played for this team in ’09, it’s entirely possible that none will be on the next contending Padres team. Keep an eye on Edward Mujica, with a 34/7 K/UIBB ratio in 42 2/3 IP; a Bell trade would likely make him the closer.

#29: Pittsburgh Pirates (me: 690 RS, 873 RA; projected: 689 RS; 709 RA). The Pirates are allowing a full run per game less than expected, which is why some of their players mistook them for a contender earlier this season. Good run prevention with a pitching staff last in the league in strikeouts is an aberration, however, and GM Neal Huntington didn’t let the short-term success get in the way of his plan. Nate McLouth, Nyjer Morgan, and Eric Hinske are gone, and Adam LaRoche, Freddy Sanchez, and Jack Wilson should follow once willing suitors are found. There’s an effective back end of a rotation to build upon with Zack Duke and Paul Maholm, but the system will have to cough up the front-end starters before the Pirates can contend. Huntington has improved the talent base in his year-plus on the job, and will continue do to so with an eye towards 2011 and beyond. That’s an infinitely better plan than Pirates fans have seen since 1992, whether their current heroes like it or not. Look for Lastings Milledge to be a boon to the team once he’s recalled.

#28: Houston Astros (me: 731 RS, 843 RA; projected: 677 RS, 733 RA). Another gap in the runs-allowed projection in the NL Central, which makes me wonder if I’m not correcting enough for the unbalanced schedule and the effects it has on the numbers. The Astros have gotten surprisingly good work from a no-name bullpen, with Chris Sampson, Alberto Arias, and Jeff Fulchino running ERAs lower than their collective Q rating, and LaTroy Hawkins turning in another solid season. With just two good starters on hand, the Astros will be leaning heavily on that pen to keep them in a weak division’s race. The offense has room to grow-eighth in OBP and SLG, just 12th in runs-which is the primary reason to be optimistic. Look for both more runs scored and allowed, and a finish within a few games of .500 on either side. It’s another contender squeezed out of an aging roster by Ed Wade. It’s also nice to see Michael Bourn fulfilling expectations after a lost 2008.

#27: Chicago White Sox (me: 739 RS, 828 RA; projected: 749 RS, 746 RA). The same question again: are the White Sox allowing fewer runs because they’re pitching and defending very well, or because they play extra games against mediocre teams? In this case, I can see an argument for the former; of six Sox starters this year, five have performed at basically league-average or better, with only Clayton Richard pitching poorly. I come back to something I’ve written again and again, which is that Ozzie Guillen can manage a pitching staff. Sox pitchers are fourth in the league in strikeouts and fourth in walks allowed, and have allowed just about a homer a game despite playing in a tough park for long balls. Add in a whole bunch of bat-missing relievers (the Sox’ top four in the pen have struck out 151 men and walked just 47 unintentionally in 134 2/3 innings), and you can keep runs off the board. They could use a major league outfielder, whether than means a healthy Carlos Quentin or something from outside the organization. Remember, Kenny Williams already made one big trade, acquiring Jake Peavy before Peavy nixed the deal, so the Sox are clearly prepared to trade tomorrow for today. All things considered, the Sox may well be the favorites to land Roy Halladay.

#26: Baltimore Orioles (me: 824 RS, 902 RA; projected: 751 RS, 858 RA). A surprisingly effective bullpen has helped the Orioles be a better run-prevention team than expected, and this is without having yet tapped the fruits of a productive farm system. Brad Bergesen, a pitch-to-contact righty, is up, but it’s the guys behind him, like Chris Tillman and Brian Matusz, who will make a big difference next year. The offense has been the real disappointment, with only Adam Jones and Luke Scott meeting or exceeding expectations. The off years by Aubrey Huff and Melvin Mora will make it harder for Andy MacPhail to get value at the trade deadline. Brian Roberts‘ down year at 31, especially a dip in speed, has to be agita-inducing for the team that extended him into his mid-30s rather than deal him away.

#25: Washington Nationals (me: 707 RS, 757 RA; projected: 709 RS, 911 RA). For the first six weeks of the season, everything went wrong for the Nationals, who were on pace to have perhaps the worst bullpen in recorded history at that point. It’s gotten a little bit better, but the failure of veteran imports Daniel Cabrera and Scott Olsen, plus those egregious failures by the pen, crushed the team early and cost Manny Acta his job. It’s not clear what long-term benefit there is in burying 24-year-old Lastings Milledge and 25-year-old Elijah Dukes in favor of older players with less upside, but they’ve done just that. Keep in mind that this team handled Ryan Zimmerman‘s stagnation as a player-he hasn’t improved a bit from the day he entered the league-by giving him a long-term contract. Want the good news? A year from now, a rotation of Steven Strasburg, Jordan Zimmerman, John Lannan, Shairon Martis, and Ross Detwiler will be young, homegrown and above-average for the NL.

#24: Kansas City Royals (me: 739 RS, 801 RA; projected: 637 RS, 781 RA). You have to try to assemble an offense this bad, and that’s exactly what Dayton Moore has done, relentlessly chasing low-OBP players to cripple his lineup. The Royals manage to strike out a lot (fifth in the AL) without gaining power (13th in SLG and HR) or walks (last, by far) in the deal. Mike Jacobs is one of the worst players in baseball, and blocking guys like Kila Ka’aihue who get on base. Jose Guillen makes $12 million this year to kill the team. There’s not some Rangersesque collection of talent on the farm. When does it get better, and under whom?

#23: Detroit Tigers (me: 776 RS, 831 RA; projected: 778 RS, 719 RA). The Tigers have allowed the third-fewest runs in the AL, and I can’t pretend to not be surprised by that. Edwin Jackson and Rick Porcello have exceeded expectations, and Adam Everett‘s presence has improved the defense behind the staff. The bullpen hasn’t been anything special, just lacking anyone having a notably bad season. The Tigers could use both a bat and an arm, the former in an outfield corner, the latter in the rotation, especially since Porcello’s use will have to monitored carefully as we head into the stretch. Without a deep farm system to pull from, it’s not clear they can add enough to sustain their lead over the White Sox and the Twins. Look for the run prevention to slip in the second half and cost them.

#22: Toronto Blue Jays (me: 738 RS, 786 RA; projected: 787 RS, 731 RA). As I’ve mentioned a few times, the Jays benefited from an exceptionally backloaded schedule that enabled them to mostly avoid the three teams in the league clearly better than them until the middle of June. Their favorable run differential reflects that early-season success against the AL West and AL Central, and the Jays were 22-12 before they ever played the Yankees, Red Sox, or Rays. They’re 22-34 since then. Some of that is a ridiculous run of pitching injuries that would have buried most any team; some of it is just playing better competition. In a vacuum, they’re one of the 10 best teams in baseball, but they don’t play in a vacuum, they play in the AL East. If they trade Roy Halladay-and they should-they could slip behind the Orioles by the end of August.

#21: Seattle Mariners (me: 641 RS, 671 RA; projected: 641 RS, 674 RA). That the Mariners have an even worse offense than I projected them to have is a bad, bad sign. Mind you, that projected record is inflated by Russell Branyan having one of the best years in the league. The rest of the offense is just awful, with five regulars (seven if you count Ronny Cedeño and Rob Johnson) posting sub-.300 OBPs. They’re hanging around thanks to a terrific outfield defense and two of the best starting pitchers in the league in Felix Hernandez and Erik Bedard. That’s not enough to win with, and Jack Zduriencek almost certainly knows that. Branyan, Jarrod Washburn, and Miguel Batista have to be trade bait over the next two weeks, no matter who it ticks off.

#20: Texas Rangers (me: 860 RS, 888 RA; 801 RS, 737 RA). The Rangers haven’t allowed fewer than 750 runs in a full season since 1990. This year isn’t going to change that, no matter what kind of pace they’re on at the moment. The improved defense, largely the result of getting Michael Young off of shortstop and Josh Hamilton out of center field (due to injury), is real. As Hamilton returns and Elvis Andrus goes through a Texas summer, balls will begin falling in for hits. Starters Kevin Millwood, Scott Feldman, and Vicente Padilla can’t sustain their ERAs given their underlying performances. The back end of the bullpen is good, but that won’t be enough as the rotation knocks them out of games early. The X factor is Roy Halladay, a pitcher the Rangers can afford both talent-wise and financially, and who would make them the favorites in the West over the Angels. Unless they make that kind of addition, however, they’ll slip under .500 by the end of the year.

#19: St. Louis Cardinals (me: 772 RS, 788 RA; projected: 717 RS, 668 RA). The surprisingly effective pitch-to-contact rotation from last year has been bolstered by the return of Chris Carpenter, who has been one of the best starters in the league on a per-inning basis. Joel Piniero has allowed just three homers and 12 walks in 115 1/3 innings, numbers that wouldn’t look out of line in the middle of Greg Maddux‘s peak. Ryan Franklin, All-Star, has been discussed plenty in this space and others. Albert Pujols is having the best year of his career to date, and is in line to be intentionally walked more in one year than any non-Barry Bonds batter in history. The Cards need all of this overachievement to continue, because the roster past Pujols, Carpenter, Adam Wainwright, and Yadier Molina is not impressive at all. That’s a terrific core, enough to contend, but to win the Cards need another bat-Troy Glaus returning healthy would help-and probably at least one more pitcher, especially a reliever. There’s just too many places where they can expect regression to not work on patching the holes that exist.

#18: Milwaukee Brewers (me: 756 RS, 761 RA; projected: 757 RS, 766). They’re a .500-ish team playing .500-ish baseball in a division likely to be won by a .500-ish squad. Trevor Hoffman hasn’t allowed a home run in 26 1/3 innings, and as the Phillies showed last season, if your homer-prone closer has a fluke year in that department, you can do some things. All they do at the plate is draw walks and hit homers-11th in batting average, 14th in doubles, and last in steals-but they do these things well. Somebody with a surname beginning with H has to start H‘ing, because the gap between where they are now and the postseason is basically the gap between Bill Hall, J.J. Hardy, and Corey Hart and effectiveness. They could sustain their runs-allowed pace in the second half but in a totally different shape, as Dave Bush and Manny Parra improve and the bullpen regresses. The Brewers have the widest range of possibilities of any of the three NL Central contenders; they could hit and win 88, or the pitching could implode and push them under .500.

#17: Colorado Rockies (801 RS, 809 RA; 814 RS, 746 RA). As mentioned, the improved defense with the return of Troy Tulowitzki, the use of Clint Barmes at second base and an assortment of strong defensive outfielders has pushed them into contention. They don’t strike batters out (11th in the NL), so they have to make plays. An underrated factor has been the return of Todd Helton, who has a .399 OBP. Not historically a patient team, the Rox are third in the NL in walks and fifth in OBP, despite just a .259 batting average, which is nothing short of lousy for a team playing half its games in Coors Field. Helton, Tulowitzki, Dexter Fowler, Seth Smith, Chris Iannetta, Brad Hawpe… this is a deep-count team that understands the value of patience and pitch selection. To beat out the Giants and the NL East teams, they’ll need some pitching help-the bullpen isn’t a strength, with the bridge to Huston Street an unsteady one at best.

#16: San Francisco Rockies (657 RS, 658 RA; 677 RS, 596 RA). As good as the pitching was expected to be, it’s been better, as Matt Cain has become #1A to Tim Lincecum‘s #1, and the worst starter, Barry Zito, has settled in between “average” and “replacement level.” Every single bullpen addition, from the pricey (Jeremy Affeldt) to the inexpensive (Justin Miller, Brandon Medders) has worked out as well. The problem is that the Giants make the Royals look patient at the plate, with just 200 bases on balls all year, and a resultant .315 OBP. The pitching is overachieving a bit, so Brian Sabean has to find a bat, and lucky for him he can replace any of seven starters and improve the team. That’s right: Brian Sabean can acquire most any decent hitter and make his team better. If he adds two, he can win the NL Wild Card. The problem for him is that he has a top-heavy farm system that makes any trade for a short-term bat very, very expensive. Do you move Angel Villalona for two players if those two players put you into October with Lincecum, Cain and Jonathan Sanchez as your rotation? Flags fly forever, and I’m not convinced this isn’t a case to try and grab one. Villalona for Adam Dunn and Cristian Guzman? For Aubrey Huff and Brian Roberts? For Matt Holliday and Jason Giambi? For Victor Martinez and Jhonny Peralta? You have to find out what’s out there as long as it doesn’t involve Madison Bumgarner, Buster Posey, or Tim Alderson.

We’re on to the top half of the league tomorrow.