If you wish a unit to march when a non-fleeing enemy unit is within 8", it will first have to take a Leadership test. If the test is passed, the unit disregards the nearby foe and marches as ordered. If the test is failed, the unit will only be able to move normally. Note that if a unit attempts this test and fails, it is still treated as having marched, even if its controlling player then elects not to have the unit move at all.