The San Francisco Giants just had a great game, why did their price go down?

Price is based solely on market pressure, so an athlete or team's on-field performance does not directly impact their price until Earnings Day. It's important to note that the Giants price will ALWAYS match their performance on Earnings Day. Here are a couple examples of market pressure:

• The SF Giants are trading at $121. To justify that price, they need: 85 regular season wins, to qualify for the playoffs, 4 post season wins, and to win their division series. To date, they have 25 regular season wins, translating into $25 of earnings. If more traders think the Giants won't make the playoffs and earn $121, they will short them and drive the price down - even if they just had great game.
• Traders bought the SF Giants in the $100 - $105 range. They have enjoyed watching the price go up over the past couple weeks, but think the Giants current price of $121 is a bit high - even though they just had a great game. They decide that it is a good time to sell their shares and lock in some profits. The sell pressure drives the stock price down.
• The Giants will be facing some tough opponents in the next couple games and a bunch of traders think the probable losses will drive their price down. They decide to sell their shares (driving the price down) while everyone is riding the high from their great game.

Jarvis Hayes has earned $68, so why is he trading at $60?

Traders may be pursuing other stocks with higher returns. This is a great opportunity to lock in some risk-free gains.

It was announced yesterday that Mark Prior is injured, why did his price go up today?

Injuries that affect a player's earning ability are a great shorting opportunity. Let's take a look at how trader activity might drive market pressure:

• Yesterday, traders shorted Prior on news of his injury, driving his price down. Today, traders covered their short positions, which pushed his price up. Remember, covering a short has the same market pressure as making a buy.
• Why would a trader cover their position? A trader may cover their position for a variety of reasons: they want to invest their money in another stock, they think Prior will be coming back this season, they see the price moving upwards and want to lock in any gains, or the price has risen above the price at which they shorted the stock so they might as well close it out. Better luck to you if you fall in the last category.
• What happens to his price if he's out for the season? Check out more info on Retiring Stocks.

Why didn't my trade go through at the price quoted?

The "Quote Box" lets you know the current price of a stock, but prices can move quickly (and volatility) on the market - especially for new IPOs. Trades are executed in the order received, so if other traders place orders just before you, your trade may go through at a slightly higher or lower price than you saw in the Quote Box.

I just bought a stock and when I clicked back to My Portfolio, the price had gone down. Why?

That's the spread. Think of it as a minimal transaction fee to keep traders honest.