Hayabusa seat reservation...

Hi,
I know from before that traveling on the Hayabusa shinkansen trains need seat reservation, even if using a JR Pass.

One time I was in a hurry because of a delayed local train to Sendai when going back to Tokyo from a daytrip and there were two trains, one Hayabusa and one slower (dont remember the name) leaving very soon. The Hayabusa train had no seats so I had to rush for the slower train.

Some times before I also experienced a full train on the Hayabusa which is understandable of course but is it possible to take a standing "seat" or would I be expected to be thrown off for that even if carrying a JR Pass?

If the train is fully booked, you will be given a standing seat ticket at the ticket counter when you book (instead of a reserved seat ticket). It is unclear whether it is possible to ride standing with JR Pass alone, and in particular standing seat tickets are not equivalent to non-reserved seat tickets, in that they are only issued if the train is full (so it's not an option you can just choose when you want to save money).

So, if at all possible, do obtain a ticket.