YW.
You don't sound dumb. Although I know what these things are, I have made a similar mistake recently of not realizing that one was taking place and it cost me. I vowed to never let it happen again.
Here is an article that may help. The idea was to go from a total outstanding shares capitilization of stocks weighted in the index to capitilization based on the actual float that is traded. This removes the influence of shares that are owned by controlling "families" and rarely trade. WMT and MSFT were two of the biggest that would be negatively impacted by this rebalance. C and XOM gained.
http://www.northerntrust.com/library/corporate/whitepapers/SPFreeFloatWP.pdf
Look at the "closing" print on MSFT - it did 21,000,000 shares on that print alone. "Someone" had to exit and eat the drop near the low of the week, and "someone" was more than happy to take it off their hands after about .70 lower from the beginning of the week.
As for trading on these exp days, there are always stocks that have and edge to them, but you have to know how to find them. Look at QCOM and study why you should have been in it if long is the direction you wanted
that day. BTW, I missed QCOM too and I even had it on my montage, but today I know I shoulda nailed it. I have commited the lesson to long term memory.
Finally I will say this. There are only two ways you can play defense in trading, by trading small size, and/or to try some sort of hedge. All you did was play offense with your whole body on a day that probably required you to dip your toes in.
nitro
Quote from giannos:
Nitro:
thanx for the post......At this point I really dont care about sounding "dumb"....But what is the SP rebalancing?.....Also I know it was triple witching day..... what is the proper play for a newbie on such days 
