If the referee thinks that this play (in his area) is legal, it's legal. For you to throw a flag there is wrong. To throw a flag you must be sure that something is a foul. If you are guessing or are unsure, it's not a foul. And if you're poaching out of your area, then you'll have more problems -- with coaches and especially your partners.
If you throw a flag there and the referee finds it to be a legal play, he will pick up your flag and have a nice chat with you, like Ed said.
The nice thing about football is that we don't have to and aren't expected to cover the entire field.
Speaking of white hat, I wore one tonight -- my first varsity white hat, although I've worn the hat many times at lower levels. 54-0 with a clock operator that understood how to ignore the habitual clock-stopping we all did, even though by rule the clock ran unstopped almost the entire second half.
And keep your hand away from your flag until you're 100% sure it's coming on the field. You'd be amazed at how coaches can see that -- it's almost like they're watching the officials or something
Rich