I look at the 6 month chart of a stock.If the level of volume seems to spike on the day of the drop, it has to be large share holder's selling. The average invester's shares would not make a dent in the closing price.
Please explain your thinking a bit further, it isn't apparent why that would be the case, nor did the volume seem that high as compared to everyday volume levels not that long ago.
If institutions were selling, we'll know it soon enough -- perhaps you'll be proven right. Perhaps wrong.
But what is the logic you employ? If daily volume is greater than some constant X value, then institutions must be selling?