Momentum investors love to back companies with the wind in their sails. Contrarian investors typically pick up the cigar butts the market has tossed aside. So what do you call investors who turn against winners? Sourpusses? Shorts?

Over on Motley Fool CAPS, we sometimes call them the savviest investors around. When one of our All-Star players -- ranked in the top 20% of our investing community -- sours on a top-rated stock, perhaps we should take notice. Maybe the player has found a chink in that highflier's armor, or a question mark in its financial footnotes. Or maybe it's just a hunch. That's why these tables aren't lists of stocks to buy or sell -- just starting points for further research.

Here's a list of stocks that some All-Stars have recently spurned:

Company

CAPS Rating (Out of 5)

1-Year Return

CAPS All-Star

Player Rating

Chicago Bridge & Iron (NYSE: CBI)

*****

123.4%

bu1le7

98.76

Southern Copper (NYSE: PCU)

*****

121.8%

hammerNnails

85.63

CNOOC (NYSE: CEO)

*****

83.6%

cincyfocusedfund

99.38

Cogent (Nasdaq: COGT)

****

2.0%

Jdbh

92.54

Banco Bilbao Vizcaya Argentaria (NYSE: BBV)

****

1.7%

introscop

91.77

Considering that, on average, 96% of CAPS' investors think these companies will outperform the market, what might have turned some of CAPS' top players against these otherwise widely admired companies?

Digging for gold in copper
The price of copper has risen to record highs over the past few years, as laborers seeking shorter work weeks and more benefits in various South American countries have fomented unrest. For example, work stoppages in Peru, the third largest producer of copper, have plagued companies such as Southern Copper, even as demand for the metal has soared. But even with copper prices down 20% from their highs earlier in 2007, they're still holding strong above $3 per pound. That's moved the company's profits -- and the stock price -- sharply higher.

Yet some CAPS investors think the labor unrest will take its toll on this premier copper producer. For example, CAPS player billat2000 thinks competitors such as Companhia Vale do Rio Doce (NYSE: RIO), BHP Billiton (NYSE: BHP), and Jiangxi Copper present better opportunities: "This company will be plagued by [strikes] and worker problems for the foreseeable future. JIXAY, BHP and RIO are much better choices for raw materials and all three of these supply China and India."

Others, such as msukkel, view China as the determining factor in future growth. With its expanding economy, China has been soaking up supply for numerous commodities, but msukkel sees the country as having satiated its demand for copper. "Seems China has most of the copper they were looking for," he writes. "I think Nickel will be the next hot [alloy] they'll (China) be eating up."

As with most commodities, success comes down to supply and demand. CAPS All-Star reddingrunner asks investors to consider the potential of copper demand versus growth in the S&P 500: "Simple math: how much do you think the S&P will increase over the next five years and how much do you think the demand for copper will increase over the same time period. With its current good valuations: advantage PCU."

Make lemonade from lemons
At Motley Fool CAPS, we invite you to share your thoughts and insights and add your voice to the debate. Go ahead -- have your say. We're eagerly waiting!

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Fool contributor Rich Duprey does not have a financial position in any of the stocks mentioned in this article. You can see his holdings here. The Motley Fool has a disclosure policy.