Come on, seriously - the gulls are smart but would they really be dissuaded by a few guys in orange shirts on the grass?

I say "nay" - this is actually a set of behaviors engineered by park owners - specifically I suspect some kind of ultrasonic deterrent (or perhaps something more sinister that might not necessarily be ok for humans!) ... I think we should get a local news team to investigate!!

I always assumed that during the 7th inning stretch or after the third quarter of the football games was when they gathered because the stadium consession stands start breaking down for the day right around then. Ever notice the excess clouds of smoke that start billowing out right around then? Breaking down the friers and what not... They do do the same thing at all the schools too though so who knows.

I think it's much simpler than that. I believe the scout birds' cue is when people start leaving the stadium in significant numbers, which tends to be around the same time as the 7th inning stretch. Sorry to dispel the myth that only Dodger fans leave early, but it has been my experience in stadiums all over the country, and San Francisco is no exception, that as a game winds down a noticeable segment of the audience leaves 'to beat the traffic'. As cars start leaving the parking lot, especially at night), it's obvious to birds, planes, superman, and anyone else paying attention that feeding time is approaching. Then the scout birds alert the rest of the flock and they begin to mass at the rim of the venue. Always a good idea to keep your hat on for extra innings...

I don't know if that's true or not. Look at this video of the seagulls here at the ballpark when there is no game.
http://www.youtube.com/watch?v=mGdsUKj8ZI0

They are hovering all over. What's the reason for this?

Well, then you need to do a scientific experiment.. have the crowd do a 3rd-inning stretch in a game and see if the gulls come!

could it be using their eye sight?
if left a slice of bread on the beach....and did not leave.....will it come and steal that slice of bread?
well yea.....

People go to any bay area elementary school and you will see they do the same thing once lunch ends.

Yes, but the question wasn't about football, a sport which has its own distinct rhythm... such as being run to a clock for the most part. (And of course there is half-time and the two-minute warning.) Perhaps the seagulls have a rudimentary ability to read the clock itself. I am serious. They sure do seem to get upset and angry whenever there is a tied game going into the tenth inning in baseball.

They're hopin' Timmy left a little plant matter behind!

Oh come on! The birds do the same thing towards the end of football games when there is no 7th inning stretch-like cue from the crowd. That can't be the main explanatory factor.