The enemies' movements are similar to those used in a skirmish you once studied. You use knowledge of it to outmaneuver a foe.

Encounter
Immediate Reaction      Melee 1

Trigger: An enemy enters a square adjacent to you or to an ally adjacent to you

Target: You or the ally

Effect: The target shifts 1 square and gains a +2 bonus to all defenses until the end of your next turn.

Published in Player's Handbook 3, page(s) 170.