I added the note that the Enrage check only happens during the Guard Assignment phase and a reminder in the Hero Wins section of the Combat phase so people aren't confused when their Hero Counter lowers a Guard Health below its Rage during Combat.

From the rules, 

in the Guard Assignment phase

💢 Enrage Check: If the Guard’s Rage is equal to or greater than its current Health, it becomes Enraged for the rest of the round. All of its Enrage abilities are active during this state. At the end of the round, reset its Rage to 1.

o Note: This is the only time during a round that Enraged is checked.

under Hero Wins section of Combat phase

If the damage from the Counter lowers the Guard’s Health below its current Rage, it does not become Enraged this round. Enrage only triggers if the condition is met during the Enrage Check of a Guard Assignment phase.