The law of TV/Movies which causes "Bad Guys" to be wildly inaccurate and "Good Guys" to be highly accurate under most circumstances. However, it is really an effect of the numbers of targets and attackers rather than the ethicality of the people involved. The Stormtrooper Effect is named after the Imperial Stromtroopers in Star Wars, a whole battlestationful of them couldn't hit a small group of rebels.
The equation can be arrived at by starting with
where P is the probability of a hit and Nt and Na are the numbers of targets and attackers respectively. Now a fairly safe assumption of the constant of proportionality is the difficulty for one attacker to hit one target under the same circumstances (Which we will denote P1). This gives us
Since "Good Guys" normally come in small groups or alone, and "Bad Guys" tend to come in hordes, we see how the Stormtrooper effect seems to be based on ethics. Of course, given that ethics are fairly subjective (both sides could be perceived as either good or bad depending on the viewer) it would be difficult to derive accuracy from that, but numbers of participants is nice and quantitive.
The Stormtrooper Effect is sometimes also known as The 16th Law of Anime or The Inverse Accuracy Effect