Bridges usually get you from one place to another. This one just gets you.

Ensnaring Bridge

Creatures with power greater than the number of cards in your hand can't attack.

"I expected a fight, but I didn't expect it from the building itself."
—Gerrard

Mystery Booster 2

The way out lay across a slender bridge of stone. It was an ancient defense of the Dwarves that could only be traversed in single file.

Tales of Middle-earth Commander

"When I said I needed a hand, I didn't mean this."
—Gerrard Capashen

Double Masters

Ensnaring Bridge's effect checks the number of cards in your hand only while a player (including you) is declaring attackers. Once a creature has legally attacked, changing its power or the number of cards in your hand won't remove it from combat.