A fighter can make this reaction when an enemy fighter finishes a move action within 3" of them. Note the distance between this fighter and the enemy fighter that made the move action. Remove this fighter from the battlefield and then set this fighter up on a platform or the battlefield floor no further from the enemy fighter that made the move action.
Building an army? Create, validate and share your list with New Recruit, army builder for Warhammer Age of Sigmar: Warcry and many more games.
Try the builder