At the end of June fund managers that follow the index will re-organzie their portfolio and are 'forced' (by their policies) to buy into all of stocks that are included in the index.
SF will be in the Russell 2000 index.
This means that on the last day (I think June 28th) there will be a huge peak in terms of volume. This happens during the last 30 minutes during that trading day and they often have to pay a premium in order to fill their 'slots'.
All imo - of course.
Also interesting is that traditionally stocks that are included in the index have a run up in the weeks before the re-constitution and are performing better over the year than the index itself (all on average of course).