As Bigby's interposing hand, except the forceful hand pursues and pushes away the opponent that the character designates. Treat this as a bull rush with a +14 bonus on the Strength check (+8 for Strength 27, +4 for being Large, and +2 for charging bonus, which it always gets). The hand always moves with the opponent to push him back the full distance allowed, and it has no speed limit.
A very strong creature could not push the hand out of its way (because the hand would instantly reposition itself between the creature and the character), but it could push the hand up against the character by successfully bull rushing the hand.