At the beginning of each round of close combat, each engaged unit with the Primal Fury special rule must take a Leadership test. If the test is passed, that unit is subject to Hatred of all units they are fighting until the end of the close combat phase. They will re-roll failed To Hit rolls even if it is not the first round of combat.
In addition, units that pass their Primal Fury test on a roll of a double 1 are subject to both the effects listed above and the Frenzy rule until the end of the close combat phase. Beastmen may become Frenzied in this way even if they have lost a combat earlier in the battle.