Amateurs control the open. Professionals control the close.
In order to understand the reason why professionals and insitutional traders control the close, you must first understand the
VWAP or volume weighted average price.
VWAP is defined as the average price of the stock traded for the day when volume is weighted.
Insitutional traders are compensated when they are able to beat the
VWAP. They will usually hold onto inventory until the end of the day so they can improve their
VWAP. This is not always the case, but because they trade in massive volume there is a good chance that they are able to get fills that will improve their average price.
It is common to see a light pullback during the doldrums after a morning rally, then a continuation of the trend into the close. If an institutional trader has buy orders stacked but is unable to get a fill during the morning rally, he will be forced to buy pushing prices higher into the close.
Source:
The Market Maker's Edge by
Josh Lukeman