Obstacles are things such as hedges, fences, walls and trenches that troops must clamber over to cross. Although obstacles may be similar in some respects to difficult ground, in that a hedge and a wood might both contain trees, there is an important difference. Obstacles are basically linear barriers, such as a wall, which troops must cross over before they can proceed. Difficult terrain describes an area of ground, such as a bog or marsh, that slows down a unit's overall speed.
It takes a model half of its move to cross an obstacle, So if a model has Move 4 it must surrender 2" to cross a hedge or a wall.
As long as the ranks on both sides are in contact with the obstacle, this is perfectly acceptable. Once the troops have moved over the obstacle, the unit's ranks are returned to base contact. Remember that the unit suffers a half move penalty until all its troops have crossed the obstacle.
If a wall, hedge or fence has a gate in it then it is assumed to be open unless otherwise agreed, and troops may move through the gate without penalty.
If a unit's formation is divided by an obstacle then it may not manoeuvre by turning or wheeling, and it may not change its formation or reform. The unit must cross the obstacle before it can do any of these things. The unit may charge, but it must completely clear the obstacle before wheeling towards the enemy.