Instantaneous Rage

rage or frenzy ability,

Your rage begins at any time you wish, even when it's not your turn or when you're surprised. You can activate your rage as a free action in response to another's action. Thus, you can gain the benefits of rage in time to prevent or ameliorate an undesirable event. For example, you can choose to enter a rage when an enemy attacks you, or casts a spell at you (to gain the benefits of a higher Constitution or your bonus on Will saves) before you know the results of the attack. You must be aware of the attack, but you may be flat-footed.

You enter a rage only during your turn

Your rage begins at any time you wish, even when it’s not your turn or when you’re surprised. You can activate your rage as a free action in response to another’s action. Thus, you can gain the benefits of rage in time to prevent or ameliorate an undesirable event. For example, you can choose to enter a rage when an enemy attacks you, or casts a spell at you (to gain the benefits of a higher Constitution or your bonus on Will saves) before you know the results of the attack. You must be aware of the attack, but you may be flat-footed.

You enter a rage only during your turn

You activate your rage instantly.