Last night's Home Run Derby at Detroit's Comerica Park gave baseball fans around the globe reason to cheer. The real fireworks begin tonight, though, when News Corp.'s (NYSE:NWS) Fox will broadcast Major League Baseball's All-Star Game -- the 76th installment of the annual midsummer classic. This year, Boston's Terry Francona will fill out a lineup card stacked top to bottom with the elite stars from the American League to compete against his counterpart, St. Louis' Tony LaRussa, and an equally imposing cast of players selected from the National League.

As the managers who guided their teams into last year's World Series, these two have been given the privilege of representing their respective leagues in tonight's contest. Meanwhile, the game's other managers will be given a few days off to reflect on what needs to be done in order for them to have the right to watch next year's game from the dugout -- in other words, contemplate what midseason changes are needed to propel their club to the top of the standings.

As investors, we should also take this time to assess the players in our portfolios. Many wait until the end of the year to do such financial housekeeping. But if there's a problem that needs to be addressed, why wait another six months to fix it?

Of course, at this point in the season, it will be relatively easy to identify which members of your team simply aren't getting the job done. Maybe you acquired a seasoned veteran like Motley Fool Income Investor pick Merck (NYSE:MRK) to anchor your lineup, but it hasn't exactly been knocking the cover off the ball. Now may be the time to decide whether such picks deserve a few more games to correct their mechanics, or a spot on the bench to make room for someone else. As manager, that's your call.

Likewise, while baseball executives are looking to sign a versatile middle infielder, dependable relief pitcher, or whatever else is needed to shore up any weak spots, investors should be looking for new prospects to round out their teams--maybe even an up-and-coming rookie like Motley Fool Hidden Gems watch list company Vasco Data Security International (NASDAQ:VDSI).

These types of changes, while vital to developing a winning long-term record, are usually obvious. It's important not to neglect those that are often overlooked. When dumping some of your laggards for a player to be named later, don't forget to rebalance your portfolio. Just as baseball managers must sometimes shuffle their lineups to achieve maximum efficiency, investors need to occasionally adjust their asset allocation weightings to keep their portfolios from getting out of whack.

Consider this hypothetical $10,000 investment:

  • Large-cap stocks -- $4,000 (40%)
  • Small-cap stocks -- $2,000 (20%)
  • International/global stocks -- $1,000 (10%)
  • Investment-grade bonds -- $3,000 (30%)

Based on risk tolerance, time horizon, and other factors, this investor felt comfortable with a 70/30 split between equity and fixed income holdings. What might this portfolio look like, though, after a year when stocks raced ahead and bonds fell out of favor?

  • Large-cap stocks -- $4,800 (39.0%)
  • Small-cap stocks -- $3,000 (24.4%)
  • International/global stocks -- $1,700 (13.8%)
  • Investment-grade bonds -- $2,800 (22.8%)

Well, the good news is that the portfolio as a whole has performed very well. However, that original 70/30 balance is now closer to 80/20 -- quite possibly too aggressive. With the mix having deviated so sharply, it may be prudent to sell a portion of the stock portfolio to bring the asset allocation back in sync with what was originally intended to be.

Of course, aside from qualified retirement accounts, there will likely be tax considerations and transaction costs to weigh. For this reason, it may sometimes be more advantageous to rebalance by directing new investment dollars toward underweighted areas rather than selling overweighted ones at a gain. Not only will the process of rebalancing prevent a portfolio from becoming lopsided -- it will also automatically harvest profits.

Before the second half of the season gets underway, take stock of your stocks and make sure you have the right ones on the field to compete.

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Fool contributor Nathan Slaughter has his fingers crossed for a decisive NL victory this year. He owns none of the companies mentioned.