First, I'm no lawyer either, haha. But yes I agree, cross examination is what happens when the defense asks questions of the prosecution's witnesses (and vice versa). First half of the trial the prosecution brings witnesses that they have coached and prepared for testimony, the whole point is to bring witnesses that make the defendant look bad and make your case against the defendant look good. The defense gets their chance to do the same later on. After the prosecution questions the witness they brought to the trial, the defense can then cross examine the witness, and obviously their objective is to try to add clarity to whatever they just said, or to take credibility away from it, basically the prosecution should be piling on damage against the defendant and cross examination should be to control the damage, or try to minimize it a little. Second half of the trial roles are reversed for the two sides.
My point of that part of my post, was that interestingly last week, a witness called by the prosecution, Dr. MacKenzie, in response to the prosecution's questions, testified that trained officers must provide medical attention and that simply calling an ambulance is not enough. Under cross examination the defense got her to qualify that statement and clarify that if the situation wasn't safe you couldn't do CPR, if there were a threatening crowd for example. But then, the defense wanted to go further with their questioning of Dr. MacKenzie and ask about fentanyl mortality. Because it wasn't part of the prosecution's original line of questioning they objected to the question (because they know it will hurt their case), so the defense lawyer said, okay, I want to call Dr. MacKenzie next week when it's my turn to call witnesses. In other words, I'm going to ask her these questions anyways because she's going to help our case.
Edit: In other words, if a witness the prosecution has selected to make the defendant look bad turns out to be so good under cross examination for the defense's case that they want to call them as their own witness later in the trial, then that's doesn't bode well for how this is going for the prosecution.