Unless the combat is a draw, each unit belonging to the losing side must make a 'Break' test. To make a Break test, roll 2D6 and modify the result by adding the difference between the winner's and the loser's combat result scores.
Then, compare the result to the unit's Leadership characteristic (remember, a unit that contains models with different Leadership values will always use the highest):
If the result of the natural roll is higher than the unit's Leadership, the unit 'Breaks' and flees.
If the result of the natural roll is equal to or lower than the unit's Leadership, but the modified result is higher than the unit's Leadership, the unit Falls Back in Good Order.
If the modified result is equal to or lower than the unit's Leadership, or if the roll is a natural double 1, the unit Gives Ground.
Note that, unlike other tests you may be required to make, a Break test has three possible outcomes. These are intended to reflect the way in which opposing battle lines push forward and are pressed back before ultimately becoming overwhelmed and breaking.