One of my favorite rules of evidence which I use very frequently in objections is the Pennsylvania Rules of Evidence 611(a). The objection relates to an individual who is a witness who is assuming facts not placed into evidence.
What this means is that a question which assumes the existence of a fact not established by the evidence is improper, as the court in Commonwealth v. Rivers from 1994 determined. The court may however, entertain assuming facts not in evidence, if the attorney represents that the assumed fax will be proven later. Such a representation however should not be made if it cannot be fulfilled, as the court in Commonwealth v. Williams from 1979 stated. In fact, the court stated that it was unprofessional conduct to ask a question which implies the existence of a factual predicate which the examiner cannot support by evidence.
Frequently, this happens when a prosecutor asks a cop in a Chester County DUI, "When did you know that the driver was drunk?" You can't say that. He can point to signs of intoxication, but he's not a medical expert or a lab test. He can say, "Did you come to a conclusion, based on your observations, that the client was incapable of safe driving?", but you can't say the person was drunk.
The law essentially has stated that an attorney, in asking a question that assumes facts not in the into evidence, must have a "good faith" basis before asking any question on cross examination. The rule is tremendously important as it's designed to prevent the irresponsible prosecutor or defense attorney from salting or planting a fictitious accusation in the minds of the jurors by framing a question in an inappropriate manner.
For example, in an assault case, the old standby question of "why did you stop beating your wife?" should be objected to by a Chester County DUI lawyer. Of course, this question, in a not so subtle way, implies that you were beating your wife and that piece of evidence has already been proven. Any particular cases you see the theme that there's a fact that's assumed that has not been established as you know as well as I do that beating a wife must be proved independently.