You can read about the parable that Jesus told online.
In practical, modern terms, someone who plays the good Samaritan (which is how I often hear it, along with "act the good Samaritan") stops to help a stranger. It usually applies to situations like an automobile accident. If the person does the best they can, acting as a reasonable person, they won't get sued - they are protected by what are called "good Samaritan laws."
Sadly, there were cases in which doctors would see an accident and stop to help. If the person didn't make a full recovery, he somehow felt entitled to sue the doctor for "malpractice." As a result, doctors were refusing to help accident victims they came across. And as a result of THAT, these "good Samaritan" laws were passed so people would not be afraid to try to help.
In the original quote "tried to play the good Samaritan and it went south" - it means someone tried their best to help, but it went badly wrong.
Samaritan should be capitalized.
The words "play" or "act" should NOT be read to mean it was not a good, honest effort.