If a unit wins the combat, models can be moved from rear ranks and placed in the front rank to increase the width of the formation so that more models can fight. The formation's width can be increased by up to two models on either or both flanks.
Source: Warhammer Fantasy: 6th Edition
If a unit wins the combat, models can be moved from rear ranks and placed in the front rank to increase the width of the formation so that more models can fight. The formation's width can be increased by up to two models on either or both flanks.