Albert Pujols won each of the last two Cardinal games with walk-off homers. A batter can hit a walk-off homer only in the bottom of the last inning that ends the game. Only a batter for the home team can hit a walk-off homer. Homering in the top of the last inning, even if it puts the batter's team ahead and decides the game does not count. Obviously, the winning players do not walk off the field in triumph until they have retired the home team in the bottom of the inning, so the term seems to dictate the definition but the meaning seems corrupted when compared with leadoff home run.
A leadoff home run is credited to the first batter in either half of the first inning.
Odd, isn't it?