1,591,000 was the volume after hours. Thats more than the average. But the after hours quote is unchanged. Does that mean there was huge sales but also huge purchases to balance it out? Not really familiar with after hours.
Lions Gate is part of the Russel index. The rebalancing occurs at the close so my guess is the large volume during the day is caused by people trying to position prior to it. I'm not sure what you mean by inflows or outflows to LGF. This does affect the tracking instruments, IWM for example. So typically inclusions help the short term stock price as shares need to be represented in those instruments. As a general rule, I don't like to see a stock I hold go down on large volume regardless of the reason. This is my understanding at least, hope it helps.