Key Facts are Critical to the Outcome of a Case
Key facts are facts critical to the outcome of a case.  Not only are key facts critical to the outcome of a case, these facts are also facts that bring forth the cause of action.  For instance, when the client states that he was injured when he was hit in the head by the respondent, because battery is defined as “intentionally or recklessly causing bodily injury to, or offensive touching,” on its face we have a battery.  Understanding this fact means that key facts surrounding this event would include (a) whether the contact with the client by the respondent was intentional or reckless, (b) whether the client gave express or implied consent to the contact.
Imagine a boxer who lost a boxing match trying to pursue a cause of action for battery because after-all, when the opponent recklessly flailed his punch at the client and the client found the punch to be injurious and offensive, on its face we have a battery. Yet, while a battery claim under those sets of facts seems highly unlikely to be taken seriously, what if the client was punched by the respondent under a different set of facts? Suppose the boxing match had ended and the two fighters remained in the ring to give the after-fight interview when the respondent punched the client. Under this set of facts, a possible battery claim would likely be taken seriously.
Then, we could ask if the client saw the punch coming, or if the client had an apprehension of imminent physical or bodily harm. If he did, this would give rise to a cause of action for assault.  I give this example to explain that my view of determining the key facts means that I need to understand the black letter law relative to the elements of a tort or criminal action. I need to be able to accomplish this in order to issue-spot during the interview with the client. Because of this, my steps for determining key facts are based on issue spotting, then focusing on the relevant and material facts surrounding each issue spotted.
To determine the key facts in a court opinion, I would first start by reading the entire case to understand the issues and questions at bar.  I would then use the Court’s definitions of the applicable black letter law to determine which facts are material in either proving or disproving the elements required in each count. 
Lastly, the procedural history differs from the facts of the case in that the procedural history tells us how the case has traveled through the court system.  It tells us how lower courts have ruled on the issues in the case and why. Conversely, the facts of the case remain unchanged throughout the lifespan of adjudication since these are the facts that gave rise to the particular causes of action.
 William H. Putman, Legal Research, Analysis, and Writing 265 (4th ed. 2018).
 Brian N. Siegel Et Al., Siegel’s Criminal Law 42 (1998).
 Putnam, supra at 275.
 Id.  Id. at 102.