The Seattle Seahawks won the NFC championship on a free play, this week's Coaching 101 breaks it down.
Faced with fourth down and seven, the San Francisco 49ers nose tackle entered the neutral zone. The neutral zone infraction is a five-yard penalty for the defense but for the offense it's a free play.
The play is practiced often, everyone runs deep and the quarterback pulls back in the hopes of finding an open receiver. If he does, great. It may just end up in a touchdown, like it did Sunday night. If the quarterback is intercepted or the ball is dropped, no big deal, the down is replayed due to the penalty anyways.