DCA and the 30 minute rule.

The TSA or whoever after 9/11 imposed a rule on flights in and out of DCA
that no passenger may leave their seat until 30 minutes after takeoff and 30
minutes before landing. My question is simple, what if 6 people all stand up
at once on say , a 737. Are the two cabin crew members going to be able to
do anything about it ? And yes, some of you are going to reply with the fact
that there may be air marshals on the flight, but say there wasn't - what
could 2 cabin crew really do to stop 6 people at once ?