This summary is not the rule. The rule text controls.
Any lawyer in the case can challenge a witness's credibility, even the lawyer who called that witness to testify. This means if you put someone on the stand and they say something surprising or unhelpful, you're not stuck with their answer. You can point out reasons why the jury shouldn't fully believe what they said.
This rule changed an old idea that used to exist in many courts. In the past, if you called a witness, you were basically saying "trust this person" and couldn't turn around and question their honesty. Tennessee's rule gets rid of that restriction. Sometimes witnesses don't cooperate, change their story, or say something different than expected, and this rule lets the lawyer who called them deal with that problem honestly instead of pretending everything the witness said is solid truth.