Looking for an expression...

[Rolex_Cellini]

Your idea: In a competition, or a race, if the first one/team stands the first position with a great distance, then how can we describe it?

idea behind "bring up the rear": In a competition, or a race, if the first one/team stands the first last position with a great distance, then how can we describe it?

first - last: opposites

[Tdol]

If you're bringing up the rear, do you have to be far behind?

[emsr2d2]

If you're bringing up the rear, do you have to be far behind?

No. Surely you're simply currently in last place.