After day 5 of Floyd case, all of the witnesses thus far appear to be from the prosecution.
When does the defense call their witnesses?
What determines the order in which witnesses appear in court to testify?
The prosecution chooses the order of its witnesses and must present all of its witnesses before the defense presents its witnesses, and the defense chooses the order of its witnesses.
The parties can agree, with the judge's permission, to take a witness out of order (usually for the convenience of a witness who has limited availability on a relatively minor issue).
But this is done far more often in civil cases than in criminal cases, because the defense wants to preserve its ability to argue that the prosecution failed to present evidence sufficient to prove its case beyond a reasonable doubt in its own case, which can be important in an appeal. If a defense witness is taken out of order, something that a defense witness says could inadvertently tip the balance by establishing some minor but mandatory element of some offense that the prosecution failed to include it its "case in chief".
For example, maybe the relevant statute requires that the defendant be over the age of eighteen to be guilty of a crime (e.g. statutory rape), and the prosecution forgets to ask a question about the defendant's age in their case in chief, so the prosecution fails to prove that element of the crime. If a defense witness taken out of order says that "I've known the defendant since I went to his fifth birthday party in 1980.", that could be the difference between having the case reversed on appeal and affirming a conviction on that count. So the defense is reluctant to allow its witnesses to be taken out of order.
After the prosecution has presented its "case in chief", and the defense has presented its "case in chief", the prosecution may then present rebuttal witnesses to the testimony of the defense witnesses, and often, the defense may then present rebuttal witnesses to the prosecution's rebuttal witnesses. After the prosecution completes its case in chief, the defense has the right, if it wishes to do so, to present no additional evidence whatsoever.
In a criminal trial, the prosecution often presents many witnesses and the defense often presents far fewer witnesses, but that is not a hard and fast rule.
Often the defense presents very little evidence for reasons similar to its reasons for not wanting to take a defense witness out of order.
For example, suppose a prosecution witness on a key point is not very credible. Offering a defense witness on that point who is also not very credible could bolster the jury's opinion of the prosecution witness's credibility, or could simply help to corroborate that "something" definitely happened that was memorable when the crime was allegedly committed, even if their accounts are not identical.