Pleading self-defense means admitting the crime

The accused who pleads self-defense admits the authorship of the crime. The burden of proving self-defense rests entirely on him, that he must then prove by clear and convincing evidence the concurrence of the following elements of self-defense, namely: (1) unlawful aggression; (2) reasonable necessity of the means employed to prevent or repel the unlawful aggression; and (3) lack of sufficient provocation on the part of the person defending himself.[1] The most important of all the elements is unlawful aggression,[2] which is the condition sine qua non for upholding self-defense as a justifying circumstance. Unless the victim committed unlawful aggression against the accused, self-defense, whether complete or incomplete, should not be appreciated, for the two other essential elements of self-defense would have no factual and legal bases without any unlawful aggression to prevent or repel.

Unlawful aggression as the condition sine qua non for upholding self-defense is aptly described in People v. Nugas,[3] as follows:
Unlawful aggression on the part of the victim is the primordial element of the justifying circumstance of self-defense. Without unlawful aggression, there can be no justified killing in defense of oneself. The test for the presence of unlawful aggression under the circumstances is whether the aggression from the victim put in real peril the life or personal safety of the person defending himself; the peril must not be an imagined or imaginary threat. Accordingly, the accused must establish the concurrence of three elements of unlawful aggression, namely: (a) there must be a physical or material attack or assault; (b) the attack or assault must be actual, or, at least, imminent; and (c) the attack or assault must be unlawful.

Unlawful aggression is of two kinds: (a) actual or material unlawful aggression; and (b) imminent unlawful aggression. Actual or material unlawful aggression means an attack with physical force or with a weapon, an offensive act that positively determines the intent of the aggressor to cause the injury. Imminent unlawful aggression means an attack that is impending or at the point of happening; it must not consist in a mere threatening attitude, nor must it be merely imaginary, but must be offensive and positively strong (like aiming a revolver at another with intent to shoot or opening a knife and making a motion as if to attack). Imminent unlawful aggression must not be a mere threatening attitude of the victim, such as pressing his right hand to his hip where a revolver was holstered, accompanied by an angry countenance, or like aiming to throw a pot.

[1] Rimano v. People, G.R. No. 156567, November 27, 2003, 416 SCRA 569, 576.

[2] People v. Dolorido, G.R. No. 191721, January 12, 2011, 639 SCRA 496, 503.

[3] G.R. No. 172606, November 23, 2011, 661 SCRA 159, 167-168.