Stopping Power

One example of this is Gears of War, where firing the lancer at an enemy player actually slows their movement speed drastically over time, making escape more difficult, and allowing the player to land shots more easily.  That only applied to the one weapon, but another example is the Counter-Strike games, where being hit by any shots from any weapon will instantly slow your movement, causing you to lose all momentum, making it difficult to run to cover or dodge.  A third example of this is Quake 3, where shots do not slow movement speed, but rather they physically bump or push the player in the direction the shot was traveling.  If aimed well, a player can be "juggled" in the air by rockets, or balanced on the tip of lighting from the lightning gun.